TODO (suggested by Nikolai)
1. Build query plan fro current query (inside storage::read) up to WithMergableState
2. Check, that plan is simple enough: Aggregating - Expression - Filter - ReadFromStorage (or simplier)
3. Check, that filter is the same as filter in projection, and also expression calculates the same aggregation keys as in projection
4. Return WithMergableState if projection applies
3 will be easier to do with ActionsDAG, cause it sees all functions, and dependencies are direct (but it is possible with ExpressionActions also)
Also need to figure out how prewhere works for projections, and
row_filter_policies.
wip
Contains error codes with number of times they have been triggered.
Columns:
- `name` ([String](../../sql-reference/data-types/string.md)) — name of the error (`errorCodeToName`).
- `code` ([Int32](../../sql-reference/data-types/int-uint.md)) — code number of the error.
- `value` ([UInt64](../../sql-reference/data-types/int-uint.md)) - number of times this error has been happened.
**Example**
``` sql
SELECT *
FROM system.errors
WHERE value > 0
ORDER BY code ASC
LIMIT 1
┌─name─────────────┬─code─┬─value─┐
│ CANNOT_OPEN_FILE │ 76 │ 1 │
└──────────────────┴──────┴───────┘
This table adds a new table called the `time_zones` table:
```
:) select * from system.time_zones limit 10;
SELECT *
FROM system.time_zones
LIMIT 10
┌─time_zone──────────┐
│ Africa/Abidjan │
│ Africa/Accra │
│ Africa/Addis_Ababa │
│ Africa/Algiers │
│ Africa/Asmara │
│ Africa/Asmera │
│ Africa/Bamako │
│ Africa/Bangui │
│ Africa/Banjul │
│ Africa/Bissau │
└────────────────────┘
10 rows in set. Elapsed: 0.012 sec.
```
The available timezones are parsed from under
`ClickHouse/contrib/cctz/testdata/zoneinfo` through a script
and the table content is constructed from the
StorageSystemTimeZones.generated.cpp`.
I was able to test this locally and was able to get a list of time
zones as shown above.
