Support for NULL as random seed; reordered parameters for convenience

dbms/src/Storages/StorageGenerateRandom.cpp

@@ -352,10 +352,10 @@ private:
 
 
 StorageGenerateRandom::StorageGenerateRandom(const StorageID & table_id_, const ColumnsDescription & columns_,
-    UInt64 max_array_length_, UInt64 max_string_length_, UInt64 random_seed_)
+    UInt64 max_array_length_, UInt64 max_string_length_, std::optional<UInt64> random_seed_)
     : IStorage(table_id_), max_array_length(max_array_length_), max_string_length(max_string_length_)
 {
-    random_seed = random_seed_ ? random_seed_ : randomSeed();
+    random_seed = random_seed_ ? *random_seed_ : randomSeed();
     setColumns(columns_);
 }
 
@@ -367,25 +367,25 @@ void registerStorageGenerateRandom(StorageFactory & factory)
         ASTs & engine_args = args.engine_args;
 
         if (engine_args.size() > 3)
-            throw Exception("Storage GenerateRandom requires at most three arguments: "\
+            throw Exception("Storage GenerateRandom requires at most three arguments: "
-                        "max_array_length, max_string_length, random_seed.",
+                "random_seed, max_string_length, max_array_length.",
                 ErrorCodes::NUMBER_OF_ARGUMENTS_DOESNT_MATCH);
 
-        UInt64 max_array_length_ = 10;
+        std::optional<UInt64> random_seed;
-        UInt64 max_string_length_ = 10;
+        UInt64 max_string_length = 10;
-        UInt64 random_seed_ = 0; // zero for random
+        UInt64 max_array_length = 10;
 
-        /// Parsing second argument if present
         if (engine_args.size() >= 1)
-            max_array_length_ = engine_args[0]->as<ASTLiteral &>().value.safeGet<UInt64>();
+            random_seed = engine_args[2]->as<ASTLiteral &>().value.safeGet<UInt64>();
 
         if (engine_args.size() >= 2)
-            max_string_length_ = engine_args[1]->as<ASTLiteral &>().value.safeGet<UInt64>();
+            max_string_length = engine_args[0]->as<ASTLiteral &>().value.safeGet<UInt64>();
 
         if (engine_args.size() == 3)
-            random_seed_ = engine_args[2]->as<ASTLiteral &>().value.safeGet<UInt64>();
+            max_array_length = engine_args[1]->as<ASTLiteral &>().value.safeGet<UInt64>();
 
-        return StorageGenerateRandom::create(args.table_id, args.columns, max_array_length_, max_string_length_, random_seed_);
+
+        return StorageGenerateRandom::create(args.table_id, args.columns, max_array_length, max_string_length, random_seed);
     });
 }
 

dbms/src/Storages/StorageGenerateRandom.h

@@ -1,5 +1,6 @@
 #pragma once
 
+#include <optional>
 #include <ext/shared_ptr_helper.h>
 #include <Storages/IStorage.h>
 
@@ -29,7 +30,7 @@ private:
 
 protected:
     StorageGenerateRandom(const StorageID & table_id_, const ColumnsDescription & columns_,
-        UInt64 max_array_length, UInt64 max_string_length, UInt64 random_seed);
+        UInt64 max_array_length, UInt64 max_string_length, std::optional<UInt64> random_seed);
 };
 
 }

dbms/src/TableFunctions/TableFunctionGenerateRandom.cpp

@@ -36,30 +36,30 @@ StoragePtr TableFunctionGenerateRandom::executeImpl(const ASTPtr & ast_function,
 
     if (args.size() < 1)
         throw Exception("Table function '" + getName() + "' requires at least one argument: "
-                        " structure(, max_array_length, max_string_length, random_seed).",
+                        " structure, [random_seed, max_string_length, max_array_length].",
                         ErrorCodes::NUMBER_OF_ARGUMENTS_DOESNT_MATCH);
 
     if (args.size() > 4)
         throw Exception("Table function '" + getName() + "' requires at most four arguments: "
-                        " structure, max_array_length, max_string_length, random_seed.",
+                        " structure, [random_seed, max_string_length, max_array_length].",
                         ErrorCodes::NUMBER_OF_ARGUMENTS_DOESNT_MATCH);
 
     /// Parsing first argument as table structure and creating a sample block
     std::string structure = args[0]->as<ASTLiteral &>().value.safeGet<String>();
 
-    UInt64 max_array_length = 10;
     UInt64 max_string_length = 10;
-    UInt64 random_seed = 0; // zero for random
+    UInt64 max_array_length = 10;
+    std::optional<UInt64> random_seed = 0; // zero for random
 
-    /// Parsing second argument if present
     if (args.size() >= 2)
-        max_array_length = args[1]->as<ASTLiteral &>().value.safeGet<UInt64>();
+        random_seed = args[3]->as<ASTLiteral &>().value.safeGet<UInt64>();
 
     if (args.size() >= 3)
-        max_string_length = args[2]->as<ASTLiteral &>().value.safeGet<UInt64>();
+        max_string_length = args[1]->as<ASTLiteral &>().value.safeGet<UInt64>();
 
     if (args.size() == 4)
-        random_seed = args[3]->as<ASTLiteral &>().value.safeGet<UInt64>();
+        max_array_length = args[2]->as<ASTLiteral &>().value.safeGet<UInt64>();
+
 
     ColumnsDescription columns = parseColumnsListFromString(structure, context);
 

docs/en/operations/table_engines/generate.md

@@ -10,7 +10,7 @@ Usage examples:
 ## Usage in ClickHouse Server
 
 ```sql
-ENGINE = GenerateRandom(max_array_length, max_string_length, random_seed)
+ENGINE = GenerateRandom(random_seed, max_string_length, max_array_length)
 ```
 
 The `max_array_length` and `max_string_length` parameters specify maximum length of all
@@ -25,7 +25,7 @@ It supports all [DataTypes](../../data_types/index.md) that can be stored in a t
 **1.** Set up the `generate_engine_table` table:
 
 ```sql
-CREATE TABLE generate_engine_table (name String, value UInt32) ENGINE=GenerateRandom(3, 5, 1)
+CREATE TABLE generate_engine_table (name String, value UInt32) ENGINE = GenerateRandom(1, 5, 3)
 ```
 
 **2.** Query the data:

docs/en/query_language/table_functions/generate.md

@@ -5,7 +5,7 @@ Allows to populate test tables with data.
 Supports all data types that can be stored in table except `LowCardinality` and `AggregateFunction`.
 
 ```sql
-generateRandom('name TypeName[, name TypeName]...', 'limit'[, 'max_array_length'[, 'max_string_length'[, 'random_seed']]]);
+generateRandom('name TypeName[, name TypeName]...', [, 'random_seed'[, 'max_string_length'[, 'max_array_length']]]);
 ```
 
 **Parameters**
@@ -15,7 +15,7 @@ generateRandom('name TypeName[, name TypeName]...', 'limit'[, 'max_array_length'
 - `limit` — Number of rows to generate.
 - `max_array_length` — Maximum array length for all generated arrays. Defaults to `10`.
 - `max_string_length` — Maximum string length for all generated strings. Defaults to `10`.
-- `random_seed` — Specify random seed manually to produce stable results. Defaults to `0` — seed is randomly generated.
+- `random_seed` — Specify random seed manually to produce stable results. If NULL — seed is randomly generated.
 
 **Returned Value**
 
@@ -25,7 +25,7 @@ A table object with requested schema.
 
 
 ```sql
-SELECT * FROM generateRandom('a Array(Int8), d Decimal32(4), c Tuple(DateTime64(3), UUID)', 3, 2, 10, 1);
+SELECT * FROM generateRandom('a Array(Int8), d Decimal32(4), c Tuple(DateTime64(3), UUID)', 1, 10, 2);
 ```
 ```text
 ┌─a────────┬────────────d─┬─c──────────────────────────────────────────────────────────────────┐