ClickHouse/docs/en/getting-started/example-datasets/uk-price-paid.md

---
slug: /en/getting-started/example-datasets/uk-price-paid
sidebar_label: UK Property Prices
sidebar_position: 1
---

# The UK property prices dataset

Projections are a great way to improve the performance of queries that you run frequently. We will demonstrate the power of projections
using the UK property dataset, which contains data about prices paid for real-estate property in England and Wales. The data is available since 1995, and the size of the dataset in uncompressed form is about 4 GiB (which will only take about 278 MiB in ClickHouse).

- Source: https://www.gov.uk/government/statistical-data-sets/price-paid-data-downloads
- Description of the fields: https://www.gov.uk/guidance/about-the-price-paid-data
- Contains HM Land Registry data © Crown copyright and database right 2021. This data is licensed under the Open Government Licence v3.0.

## Create the Table {#create-table}

```sql
CREATE TABLE uk_price_paid
(
    price UInt32,
    date Date,
    postcode1 LowCardinality(String),
    postcode2 LowCardinality(String),
    type Enum8('terraced' = 1, 'semi-detached' = 2, 'detached' = 3, 'flat' = 4, 'other' = 0),
    is_new UInt8,
    duration Enum8('freehold' = 1, 'leasehold' = 2, 'unknown' = 0),
    addr1 String,
    addr2 String,
    street LowCardinality(String),
    locality LowCardinality(String),
    town LowCardinality(String),
    district LowCardinality(String),
    county LowCardinality(String)
)
ENGINE = MergeTree
ORDER BY (postcode1, postcode2, addr1, addr2);
```

## Preprocess and Insert the Data {#preprocess-import-data}

We will use the `url` function to stream the data into ClickHouse. We need to preprocess some of the incoming data first, which includes:
- splitting the `postcode` to two different columns - `postcode1` and `postcode2`, which is better for storage and queries
- converting the `time` field to date as it only contains 00:00 time
- ignoring the [UUid](../../sql-reference/data-types/uuid.md) field because we don't need it for analysis
- transforming `type` and `duration` to more readable `Enum` fields using the [transform](../../sql-reference/functions/other-functions.md#transform) function
- transforming the `is_new` field from a single-character string (`Y`/`N`) to a [UInt8](../../sql-reference/data-types/int-uint.md#uint8-uint16-uint32-uint64-uint256-int8-int16-int32-int64-int128-int256) field with 0 or 1
- drop the last two columns since they all have the same value (which is 0)

The `url` function streams the data from the web server into your ClickHouse table. The following command inserts 5 million rows into the `uk_price_paid` table:

```sql
INSERT INTO uk_price_paid
WITH
   splitByChar(' ', postcode) AS p
SELECT
    toUInt32(price_string) AS price,
    parseDateTimeBestEffortUS(time) AS date,
    p[1] AS postcode1,
    p[2] AS postcode2,
    transform(a, ['T', 'S', 'D', 'F', 'O'], ['terraced', 'semi-detached', 'detached', 'flat', 'other']) AS type,
    b = 'Y' AS is_new,
    transform(c, ['F', 'L', 'U'], ['freehold', 'leasehold', 'unknown']) AS duration,
    addr1,
    addr2,
    street,
    locality,
    town,
    district,
    county
FROM url(
    'http://prod.publicdata.landregistry.gov.uk.s3-website-eu-west-1.amazonaws.com/pp-complete.csv',
    'CSV',
    'uuid_string String,
    price_string String,
    time String,
    postcode String,
    a String,
    b String,
    c String,
    addr1 String,
    addr2 String,
    street String,
    locality String,
    town String,
    district String,
    county String,
    d String,
    e String'
) SETTINGS max_http_get_redirects=10;
```

Wait for the data to insert - it will take a minute or two depending on the network speed.

## Validate the Data {#validate-data}

Let's verify it worked by seeing how many rows were inserted:

```sql
SELECT count()
FROM uk_price_paid
```

At the time this query was run, the dataset had 27,450,499 rows. Let's see what the storage size is of the table in ClickHouse:

```sql
SELECT formatReadableSize(total_bytes)
FROM system.tables
WHERE name = 'uk_price_paid'
```

Notice the size of the table is just 221.43 MiB!

## Run Some Queries {#run-queries}

Let's run some queries to analyze the data:

### Query 1. Average Price Per Year {#average-price}

```sql
SELECT
   toYear(date) AS year,
   round(avg(price)) AS price,
   bar(price, 0, 1000000, 80
)
FROM uk_price_paid
GROUP BY year
ORDER BY year
```

The result looks like:

```response
┌─year─┬──price─┬─bar(round(avg(price)), 0, 1000000, 80)─┐
│ 1995 │  67934 │ █████▍                                 │
│ 1996 │  71508 │ █████▋                                 │
│ 1997 │  78536 │ ██████▎                                │
│ 1998 │  85441 │ ██████▋                                │
│ 1999 │  96038 │ ███████▋                               │
│ 2000 │ 107487 │ ████████▌                              │
│ 2001 │ 118888 │ █████████▌                             │
│ 2002 │ 137948 │ ███████████                            │
│ 2003 │ 155893 │ ████████████▍                          │
│ 2004 │ 178888 │ ██████████████▎                        │
│ 2005 │ 189359 │ ███████████████▏                       │
│ 2006 │ 203532 │ ████████████████▎                      │
│ 2007 │ 219375 │ █████████████████▌                     │
│ 2008 │ 217056 │ █████████████████▎                     │
│ 2009 │ 213419 │ █████████████████                      │
│ 2010 │ 236110 │ ██████████████████▊                    │
│ 2011 │ 232805 │ ██████████████████▌                    │
│ 2012 │ 238381 │ ███████████████████                    │
│ 2013 │ 256927 │ ████████████████████▌                  │
│ 2014 │ 280008 │ ██████████████████████▍                │
│ 2015 │ 297263 │ ███████████████████████▋               │
│ 2016 │ 313518 │ █████████████████████████              │
│ 2017 │ 346371 │ ███████████████████████████▋           │
│ 2018 │ 350556 │ ████████████████████████████           │
│ 2019 │ 352184 │ ████████████████████████████▏          │
│ 2020 │ 375808 │ ██████████████████████████████         │
│ 2021 │ 381105 │ ██████████████████████████████▍        │
│ 2022 │ 362572 │ █████████████████████████████          │
└──────┴────────┴────────────────────────────────────────┘
```

### Query 2. Average Price per Year in London {#average-price-london}

```sql
SELECT
   toYear(date) AS year,
   round(avg(price)) AS price,
   bar(price, 0, 2000000, 100
)
FROM uk_price_paid
WHERE town = 'LONDON'
GROUP BY year
ORDER BY year
```

The result looks like:

```response
┌─year─┬───price─┬─bar(round(avg(price)), 0, 2000000, 100)───────────────┐
│ 1995 │  109110 │ █████▍                                                │
│ 1996 │  118659 │ █████▊                                                │
│ 1997 │  136526 │ ██████▋                                               │
│ 1998 │  153002 │ ███████▋                                              │
│ 1999 │  180633 │ █████████                                             │
│ 2000 │  215849 │ ██████████▋                                           │
│ 2001 │  232987 │ ███████████▋                                          │
│ 2002 │  263668 │ █████████████▏                                        │
│ 2003 │  278424 │ █████████████▊                                        │
│ 2004 │  304664 │ ███████████████▏                                      │
│ 2005 │  322887 │ ████████████████▏                                     │
│ 2006 │  356195 │ █████████████████▋                                    │
│ 2007 │  404062 │ ████████████████████▏                                 │
│ 2008 │  420741 │ █████████████████████                                 │
│ 2009 │  427754 │ █████████████████████▍                                │
│ 2010 │  480322 │ ████████████████████████                              │
│ 2011 │  496278 │ ████████████████████████▋                             │
│ 2012 │  519482 │ █████████████████████████▊                            │
│ 2013 │  616195 │ ██████████████████████████████▋                       │
│ 2014 │  724121 │ ████████████████████████████████████▏                 │
│ 2015 │  792101 │ ███████████████████████████████████████▌              │
│ 2016 │  843589 │ ██████████████████████████████████████████▏           │
│ 2017 │  983523 │ █████████████████████████████████████████████████▏    │
│ 2018 │ 1016753 │ ██████████████████████████████████████████████████▋   │
│ 2019 │ 1041673 │ ████████████████████████████████████████████████████  │
│ 2020 │ 1060027 │ █████████████████████████████████████████████████████ │
│ 2021 │  958249 │ ███████████████████████████████████████████████▊      │
│ 2022 │  902596 │ █████████████████████████████████████████████▏        │
└──────┴─────────┴───────────────────────────────────────────────────────┘
```

Something happened to home prices in 2020! But that is probably not a surprise...

### Query 3. The Most Expensive Neighborhoods {#most-expensive-neighborhoods}

```sql
SELECT
    town,
    district,
    count() AS c,
    round(avg(price)) AS price,
    bar(price, 0, 5000000, 100)
FROM uk_price_paid
WHERE date >= '2020-01-01'
GROUP BY
    town,
    district
HAVING c >= 100
ORDER BY price DESC
LIMIT 100
```

The result looks like:

```response
┌─town─────────────────┬─district───────────────┬─────c─┬───price─┬─bar(round(avg(price)), 0, 5000000, 100)─────────────────────────┐
│ LONDON               │ CITY OF LONDON         │   578 │ 3149590 │ ██████████████████████████████████████████████████████████████▊ │
│ LONDON               │ CITY OF WESTMINSTER    │  7083 │ 2903794 │ ██████████████████████████████████████████████████████████      │
│ LONDON               │ KENSINGTON AND CHELSEA │  4986 │ 2333782 │ ██████████████████████████████████████████████▋                 │
│ LEATHERHEAD          │ ELMBRIDGE              │   203 │ 2071595 │ █████████████████████████████████████████▍                      │
│ VIRGINIA WATER       │ RUNNYMEDE              │   308 │ 1939465 │ ██████████████████████████████████████▋                         │
│ LONDON               │ CAMDEN                 │  5750 │ 1673687 │ █████████████████████████████████▍                              │
│ WINDLESHAM           │ SURREY HEATH           │   182 │ 1428358 │ ████████████████████████████▌                                   │
│ NORTHWOOD            │ THREE RIVERS           │   112 │ 1404170 │ ████████████████████████████                                    │
│ BARNET               │ ENFIELD                │   259 │ 1338299 │ ██████████████████████████▋                                     │
│ LONDON               │ ISLINGTON              │  5504 │ 1275520 │ █████████████████████████▌                                      │
│ LONDON               │ RICHMOND UPON THAMES   │  1345 │ 1261935 │ █████████████████████████▏                                      │
│ COBHAM               │ ELMBRIDGE              │   727 │ 1251403 │ █████████████████████████                                       │
│ BEACONSFIELD         │ BUCKINGHAMSHIRE        │   680 │ 1199970 │ ███████████████████████▊                                        │
│ LONDON               │ TOWER HAMLETS          │ 10012 │ 1157827 │ ███████████████████████▏                                        │
│ LONDON               │ HOUNSLOW               │  1278 │ 1144389 │ ██████████████████████▊                                         │
│ BURFORD              │ WEST OXFORDSHIRE       │   182 │ 1139393 │ ██████████████████████▋                                         │
│ RICHMOND             │ RICHMOND UPON THAMES   │  1649 │ 1130076 │ ██████████████████████▌                                         │
│ KINGSTON UPON THAMES │ RICHMOND UPON THAMES   │   147 │ 1126111 │ ██████████████████████▌                                         │
│ ASCOT                │ WINDSOR AND MAIDENHEAD │   773 │ 1106109 │ ██████████████████████                                          │
│ LONDON               │ HAMMERSMITH AND FULHAM │  6162 │ 1056198 │ █████████████████████                                           │
│ RADLETT              │ HERTSMERE              │   513 │ 1045758 │ ████████████████████▊                                           │
│ LEATHERHEAD          │ GUILDFORD              │   354 │ 1045175 │ ████████████████████▊                                           │
│ WEYBRIDGE            │ ELMBRIDGE              │  1275 │ 1036702 │ ████████████████████▋                                           │
│ FARNHAM              │ EAST HAMPSHIRE         │   107 │ 1033682 │ ████████████████████▋                                           │
│ ESHER                │ ELMBRIDGE              │   915 │ 1032753 │ ████████████████████▋                                           │
│ FARNHAM              │ HART                   │   102 │ 1002692 │ ████████████████████                                            │
│ GERRARDS CROSS       │ BUCKINGHAMSHIRE        │   845 │  983639 │ ███████████████████▋                                            │
│ CHALFONT ST GILES    │ BUCKINGHAMSHIRE        │   286 │  973993 │ ███████████████████▍                                            │
│ SALCOMBE             │ SOUTH HAMS             │   215 │  965724 │ ███████████████████▎                                            │
│ SURBITON             │ ELMBRIDGE              │   181 │  960346 │ ███████████████████▏                                            │
│ BROCKENHURST         │ NEW FOREST             │   226 │  951278 │ ███████████████████                                             │
│ SUTTON COLDFIELD     │ LICHFIELD              │   110 │  930757 │ ██████████████████▌                                             │
│ EAST MOLESEY         │ ELMBRIDGE              │   372 │  927026 │ ██████████████████▌                                             │
│ LLANGOLLEN           │ WREXHAM                │   127 │  925681 │ ██████████████████▌                                             │
│ OXFORD               │ SOUTH OXFORDSHIRE      │   638 │  923830 │ ██████████████████▍                                             │
│ LONDON               │ MERTON                 │  4383 │  923194 │ ██████████████████▍                                             │
│ GUILDFORD            │ WAVERLEY               │   261 │  905733 │ ██████████████████                                              │
│ TEDDINGTON           │ RICHMOND UPON THAMES   │  1147 │  894856 │ █████████████████▊                                              │
│ HARPENDEN            │ ST ALBANS              │  1271 │  893079 │ █████████████████▋                                              │
│ HENLEY-ON-THAMES     │ SOUTH OXFORDSHIRE      │  1042 │  887557 │ █████████████████▋                                              │
│ POTTERS BAR          │ WELWYN HATFIELD        │   314 │  863037 │ █████████████████▎                                              │
│ LONDON               │ WANDSWORTH             │ 13210 │  857318 │ █████████████████▏                                              │
│ BILLINGSHURST        │ CHICHESTER             │   255 │  856508 │ █████████████████▏                                              │
│ LONDON               │ SOUTHWARK              │  7742 │  843145 │ ████████████████▋                                               │
│ LONDON               │ HACKNEY                │  6656 │  839716 │ ████████████████▋                                               │
│ LUTTERWORTH          │ HARBOROUGH             │  1096 │  836546 │ ████████████████▋                                               │
│ KINGSTON UPON THAMES │ KINGSTON UPON THAMES   │  1846 │  828990 │ ████████████████▌                                               │
│ LONDON               │ EALING                 │  5583 │  820135 │ ████████████████▍                                               │
│ INGATESTONE          │ CHELMSFORD             │   120 │  815379 │ ████████████████▎                                               │
│ MARLOW               │ BUCKINGHAMSHIRE        │   718 │  809943 │ ████████████████▏                                               │
│ EAST GRINSTEAD       │ TANDRIDGE              │   105 │  809461 │ ████████████████▏                                               │
│ CHIGWELL             │ EPPING FOREST          │   484 │  809338 │ ████████████████▏                                               │
│ EGHAM                │ RUNNYMEDE              │   989 │  807858 │ ████████████████▏                                               │
│ HASLEMERE            │ CHICHESTER             │   223 │  804173 │ ████████████████                                                │
│ PETWORTH             │ CHICHESTER             │   288 │  803206 │ ████████████████                                                │
│ TWICKENHAM           │ RICHMOND UPON THAMES   │  2194 │  802616 │ ████████████████                                                │
│ WEMBLEY              │ BRENT                  │  1698 │  801733 │ ████████████████                                                │
│ HINDHEAD             │ WAVERLEY               │   233 │  801482 │ ████████████████                                                │
│ LONDON               │ BARNET                 │  8083 │  792066 │ ███████████████▋                                                │
│ WOKING               │ GUILDFORD              │   343 │  789360 │ ███████████████▋                                                │
│ STOCKBRIDGE          │ TEST VALLEY            │   318 │  777909 │ ███████████████▌                                                │
│ BERKHAMSTED          │ DACORUM                │  1049 │  776138 │ ███████████████▌                                                │
│ MAIDENHEAD           │ BUCKINGHAMSHIRE        │   236 │  775572 │ ███████████████▌                                                │
│ SOLIHULL             │ STRATFORD-ON-AVON      │   142 │  770727 │ ███████████████▍                                                │
│ GREAT MISSENDEN      │ BUCKINGHAMSHIRE        │   431 │  764493 │ ███████████████▎                                                │
│ TADWORTH             │ REIGATE AND BANSTEAD   │   920 │  757511 │ ███████████████▏                                                │
│ LONDON               │ BRENT                  │  4124 │  757194 │ ███████████████▏                                                │
│ THAMES DITTON        │ ELMBRIDGE              │   470 │  750828 │ ███████████████                                                 │
│ LONDON               │ LAMBETH                │ 10431 │  750532 │ ███████████████                                                 │
│ RICKMANSWORTH        │ THREE RIVERS           │  1500 │  747029 │ ██████████████▊                                                 │
│ KINGS LANGLEY        │ DACORUM                │   281 │  746536 │ ██████████████▊                                                 │
│ HARLOW               │ EPPING FOREST          │   172 │  739423 │ ██████████████▋                                                 │
│ TONBRIDGE            │ SEVENOAKS              │   103 │  738740 │ ██████████████▋                                                 │
│ BELVEDERE            │ BEXLEY                 │   686 │  736385 │ ██████████████▋                                                 │
│ CRANBROOK            │ TUNBRIDGE WELLS        │   769 │  734328 │ ██████████████▋                                                 │
│ SOLIHULL             │ WARWICK                │   116 │  733286 │ ██████████████▋                                                 │
│ ALDERLEY EDGE        │ CHESHIRE EAST          │   357 │  732882 │ ██████████████▋                                                 │
│ WELWYN               │ WELWYN HATFIELD        │   404 │  730281 │ ██████████████▌                                                 │
│ CHISLEHURST          │ BROMLEY                │   870 │  730279 │ ██████████████▌                                                 │
│ LONDON               │ HARINGEY               │  6488 │  726715 │ ██████████████▌                                                 │
│ AMERSHAM             │ BUCKINGHAMSHIRE        │   965 │  725426 │ ██████████████▌                                                 │
│ SEVENOAKS            │ SEVENOAKS              │  2183 │  725102 │ ██████████████▌                                                 │
│ BOURNE END           │ BUCKINGHAMSHIRE        │   269 │  724595 │ ██████████████▍                                                 │
│ NORTHWOOD            │ HILLINGDON             │   568 │  722436 │ ██████████████▍                                                 │
│ PURFLEET             │ THURROCK               │   143 │  722205 │ ██████████████▍                                                 │
│ SLOUGH               │ BUCKINGHAMSHIRE        │   832 │  721529 │ ██████████████▍                                                 │
│ INGATESTONE          │ BRENTWOOD              │   301 │  718292 │ ██████████████▎                                                 │
│ EPSOM                │ REIGATE AND BANSTEAD   │   315 │  709264 │ ██████████████▏                                                 │
│ ASHTEAD              │ MOLE VALLEY            │   524 │  708646 │ ██████████████▏                                                 │
│ BETCHWORTH           │ MOLE VALLEY            │   155 │  708525 │ ██████████████▏                                                 │
│ OXTED                │ TANDRIDGE              │   645 │  706946 │ ██████████████▏                                                 │
│ READING              │ SOUTH OXFORDSHIRE      │   593 │  705466 │ ██████████████                                                  │
│ FELTHAM              │ HOUNSLOW               │  1536 │  703815 │ ██████████████                                                  │
│ TUNBRIDGE WELLS      │ WEALDEN                │   207 │  703296 │ ██████████████                                                  │
│ LEWES                │ WEALDEN                │   116 │  701349 │ ██████████████                                                  │
│ OXFORD               │ OXFORD                 │  3656 │  700813 │ ██████████████                                                  │
│ MAYFIELD             │ WEALDEN                │   177 │  698158 │ █████████████▊                                                  │
│ PINNER               │ HARROW                 │   997 │  697876 │ █████████████▊                                                  │
│ LECHLADE             │ COTSWOLD               │   155 │  696262 │ █████████████▊                                                  │
│ WALTON-ON-THAMES     │ ELMBRIDGE              │  1850 │  690102 │ █████████████▋                                                  │
└──────────────────────┴────────────────────────┴───────┴─────────┴─────────────────────────────────────────────────────────────────┘
```

## Let's Speed Up Queries Using Projections {#speedup-with-projections}

[Projections](../../sql-reference/statements/alter/projection.md) allow you to improve query speeds by storing pre-aggregated data in whatever format you want. In this example, we create a projection that keeps track of the average price, total price, and count of properties grouped by the year, district and town. At query time, ClickHouse will use your projection if it thinks the projection can improve the performance of the query (you don't have to do anything special to use the projection - ClickHouse decides for you when the projection will be useful).

### Build a Projection {#build-projection}

Let's create an aggregate projection by the dimensions `toYear(date)`, `district`, and `town`:

```sql
ALTER TABLE uk_price_paid
    ADD PROJECTION projection_by_year_district_town
    (
        SELECT
            toYear(date),
            district,
            town,
            avg(price),
            sum(price),
            count()
        GROUP BY
            toYear(date),
            district,
            town
    )
```

Populate the projection for existing data. (Without materializing it, the projection will be created for only newly inserted data):

```sql
ALTER TABLE uk_price_paid
    MATERIALIZE PROJECTION projection_by_year_district_town
SETTINGS mutations_sync = 1
```

## Test Performance {#test-performance}

Let's run the same 3 queries again:

### Query 1. Average Price Per Year {#average-price-projections}

```sql
SELECT
    toYear(date) AS year,
    round(avg(price)) AS price,
    bar(price, 0, 1000000, 80)
FROM uk_price_paid
GROUP BY year
ORDER BY year ASC
```

The result is the same, but the performance is better!
```response
No projection:   28 rows in set. Elapsed: 1.775 sec. Processed 27.45 million rows, 164.70 MB (15.47 million rows/s., 92.79 MB/s.)
With projection: 28 rows in set. Elapsed: 0.665 sec. Processed 87.51 thousand rows, 3.21 MB (131.51 thousand rows/s., 4.82 MB/s.)
```


### Query 2. Average Price Per Year in London {#average-price-london-projections}

```sql
SELECT
    toYear(date) AS year,
    round(avg(price)) AS price,
    bar(price, 0, 2000000, 100)
FROM uk_price_paid
WHERE town = 'LONDON'
GROUP BY year
ORDER BY year ASC
```

Same result, but notice the improvement in query performance:

```response
No projection:   28 rows in set. Elapsed: 0.720 sec. Processed 27.45 million rows, 46.61 MB (38.13 million rows/s., 64.74 MB/s.)
With projection: 28 rows in set. Elapsed: 0.015 sec. Processed 87.51 thousand rows, 3.51 MB (5.74 million rows/s., 230.24 MB/s.)
```

### Query 3. The Most Expensive Neighborhoods {#most-expensive-neighborhoods-projections}

The condition (date >= '2020-01-01') needs to be modified so that it matches the projection dimension (`toYear(date) >= 2020)`:

```sql
SELECT
    town,
    district,
    count() AS c,
    round(avg(price)) AS price,
    bar(price, 0, 5000000, 100)
FROM uk_price_paid
WHERE toYear(date) >= 2020
GROUP BY
    town,
    district
HAVING c >= 100
ORDER BY price DESC
LIMIT 100
```

Again, the result is the same but notice the improvement in query performance:

```response
No projection:   100 rows in set. Elapsed: 0.928 sec. Processed 27.45 million rows, 103.80 MB (29.56 million rows/s., 111.80 MB/s.)
With projection: 100 rows in set. Elapsed: 0.336 sec. Processed 17.32 thousand rows, 1.23 MB (51.61 thousand rows/s., 3.65 MB/s.)
```

### Test it in the Playground {#playground}

The dataset is also available in the [Online Playground](https://play.clickhouse.com/play?user=play#U0VMRUNUIHRvd24sIGRpc3RyaWN0LCBjb3VudCgpIEFTIGMsIHJvdW5kKGF2ZyhwcmljZSkpIEFTIHByaWNlLCBiYXIocHJpY2UsIDAsIDUwMDAwMDAsIDEwMCkgRlJPTSB1a19wcmljZV9wYWlkIFdIRVJFIGRhdGUgPj0gJzIwMjAtMDEtMDEnIEdST1VQIEJZIHRvd24sIGRpc3RyaWN0IEhBVklORyBjID49IDEwMCBPUkRFUiBCWSBwcmljZSBERVNDIExJTUlUIDEwMA==).