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cherry pick pingcap#2831 to release-4.0
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Signed-off-by: ti-srebot <[email protected]>
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Zejun Li authored and ti-srebot committed Jun 16, 2020
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14 changes: 13 additions & 1 deletion sql-statements/sql-statement-do.md
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Expand Up @@ -7,7 +7,13 @@ aliases: ['/docs/stable/reference/sql/statements/do/']

# DO

This statement executes an expression, without returning a result. In MySQL, a common use-case is to execute stored programs without needing to handle the result. Since TiDB does not provide stored routines, this function has a more limited use.
`DO` executes the expressions but does not return any results. In most cases, `DO` is equivalent to `SELECT expr, ...` that does not return a result.

> **Note:**
>
> `DO` only executes expressions. It cannot be used in all cases where `SELECT` can be used. For example, `DO id FROM t1` is invalid because it references a table.
In MySQL, a common use case is to execute stored procedure or trigger. Since TiDB does not provide stored procedure or trigger, this function has a limited use.

## Synopsis

Expand All @@ -25,6 +31,8 @@ This statement executes an expression, without returning a result. In MySQL, a c

## Examples

This SELECT statement pauses, but also produces a result set.

```sql
mysql> SELECT SLEEP(5);
+----------+
Expand All @@ -33,7 +41,11 @@ mysql> SELECT SLEEP(5);
| 0 |
+----------+
1 row in set (5.00 sec)
```

DO, on the other hand, pauses without producing a result set.

```sql
mysql> DO SLEEP(5);
Query OK, 0 rows affected (5.00 sec)

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21 changes: 20 additions & 1 deletion sql-statements/sql-statement-set-variable.md
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Expand Up @@ -7,16 +7,26 @@ aliases: ['/docs/stable/reference/sql/statements/set-variable/']

# `SET [GLOBAL|SESSION] <variable>`

The statement `SET [GLOBAL|SESSION]` modifies one of TiDB's built in variables, of either `SESSION` or `GLOBAL` scope. Note that similar to MySQL, changes to `GLOBAL` variables will not apply to either existing connections, or the local connection. Only new sessions will reflect the changes to the value.
The statement `SET [GLOBAL|SESSION]` modifies one of TiDB's built in variables, of either `SESSION` or `GLOBAL` scope.

> **Note:**
>
> Similar to MySQL, changes to `GLOBAL` variables do not apply to either existing connections, or the local connection. Only new sessions reflect the changes to the value.
## Synopsis

**SetStmt:**

![SetStmt](/media/sqlgram/SetStmt.png)

**VariableAssignment:**

![VariableAssignment](/media/sqlgram/VariableAssignment.png)

## Examples

Get the value of `sql_mode`.

```sql
mysql> SHOW GLOBAL VARIABLES LIKE 'sql_mode';
+---------------+-------------------------------------------------------------------------------------------------------------------------------------------+
Expand All @@ -33,7 +43,12 @@ mysql> SHOW SESSION VARIABLES LIKE 'sql_mode';
| sql_mode | ONLY_FULL_GROUP_BY,STRICT_TRANS_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION |
+---------------+-------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)
```

Update the value of `sql_mode` globally.
If you check the value of `SQL_mode` after the update, you can see that the value of `SESSION` level has not been updated:

```sql
mysql> SET GLOBAL sql_mode = 'STRICT_TRANS_TABLES,NO_AUTO_CREATE_USER';
Query OK, 0 rows affected (0.03 sec)

Expand All @@ -52,7 +67,11 @@ mysql> SHOW SESSION VARIABLES LIKE 'sql_mode';
| sql_mode | ONLY_FULL_GROUP_BY,STRICT_TRANS_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION |
+---------------+-------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)
```

Using `SET SESSION` takes effect immediately:

```sql
mysql> SET SESSION sql_mode = 'STRICT_TRANS_TABLES,NO_AUTO_CREATE_USER';
Query OK, 0 rows affected (0.01 sec)

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192 changes: 115 additions & 77 deletions sql-statements/sql-statement-show-variables.md
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Expand Up @@ -25,85 +25,123 @@ This statement shows a list of variables for the scope of either `GLOBAL` or `SE

## Examples

List all TiDB specific variables. For detailed description, refer to [TiDB Specific System Variables](/tidb-specific-system-variables.md).

```sql
mysql> SHOW GLOBAL VARIABLES LIKE 'tidb%';
+-------------------------------------+---------------+
| Variable_name | Value |
+-------------------------------------+---------------+
| tidb_ddl_error_count_limit | 512 |
| tidb_dml_batch_size | 20000 |
| tidb_force_priority | NO_PRIORITY |
| tidb_batch_insert | 0 |
| tidb_skip_utf8_check | 0 |
| tidb_backoff_lock_fast | 100 |
| tidb_opt_join_reorder_threshold | 0 |
| tidb_auto_analyze_end_time | 23:59 +0000 |
| tidb_slow_log_threshold | 300 |
| tidb_opt_correlation_exp_factor | 1 |
| tidb_mem_quota_sort | 1073741824 |
| tidb_current_ts | 0 |
| tidb_ddl_reorg_batch_size | 256 |
| tidb_checksum_table_concurrency | 4 |
| tidb_check_mb4_value_in_utf8 | 1 |
| tidb_distsql_scan_concurrency | 15 |
| tidb_optimizer_selectivity_level | 0 |
| tidb_opt_agg_push_down | 0 |
| tidb_max_chunk_size | 1024 |
| tidb_low_resolution_tso | 0 |
| tidb_index_lookup_size | 20000 |
| tidb_skip_isolation_level_check | 0 |
| tidb_opt_write_row_id | 0 |
| tidb_wait_split_region_finish | 1 |
| tidb_index_lookup_join_concurrency | 4 |
| tidb_mem_quota_indexlookupjoin | 34359738368 |
| tidb_replica_read | leader |
| tidb_ddl_reorg_priority | PRIORITY_LOW |
| tidb_batch_commit | 0 |
| tidb_mem_quota_mergejoin | 34359738368 |
| tidb_mem_quota_query | 34359738368 |
| tidb_batch_delete | 0 |
| tidb_build_stats_concurrency | 4 |
| tidb_enable_index_merge | 0 |
| tidb_enable_radix_join | 0 |
| tidb_retry_limit | 10 |
| tidb_query_log_max_len | 2048 |
| tidb_config | |
| tidb_ddl_reorg_worker_cnt | 4 |
| tidb_opt_insubq_to_join_and_agg | 1 |
| tidb_enable_vectorized_expression | 1 |
| tidb_mem_quota_hashjoin | 34359738368 |
| tidb_disable_txn_auto_retry | 1 |
| tidb_enable_window_function | 1 |
| tidb_init_chunk_size | 32 |
| tidb_constraint_check_in_place | 0 |
| tidb_wait_split_region_timeout | 300 |
| tidb_hash_join_concurrency | 5 |
| tidb_enable_fast_analyze | 0 |
| tidb_enable_cascades_planner | 0 |
| tidb_txn_mode | |
| tidb_index_serial_scan_concurrency | 1 |
| tidb_projection_concurrency | 4 |
| tidb_enable_noop_functions | 0 |
| tidb_index_lookup_concurrency | 4 |
| tidb_hashagg_partial_concurrency | 4 |
| tidb_general_log | 0 |
| tidb_enable_streaming | 0 |
| tidb_backoff_weight | 2 |
| tidb_mem_quota_topn | 34359738368 |
| tidb_scatter_region | 0 |
| tidb_index_join_batch_size | 25000 |
| tidb_snapshot | |
| tidb_expensive_query_time_threshold | 60 |
| tidb_slow_query_file | tidb-slow.log |
| tidb_auto_analyze_ratio | 0.5 |
| tidb_enable_table_partition | auto |
| tidb_auto_analyze_start_time | 00:00 +0000 |
| tidb_mem_quota_nestedloopapply | 34359738368 |
| tidb_mem_quota_indexlookupreader | 34359738368 |
| tidb_hashagg_final_concurrency | 4 |
| tidb_opt_correlation_threshold | 0.9 |
+-------------------------------------+---------------+
68 rows in set (0.01 sec)
+-------------------------------------+---------------------+
| Variable_name | Value |
+-------------------------------------+---------------------+
| tidb_allow_batch_cop | 0 |
| tidb_allow_remove_auto_inc | 0 |
| tidb_auto_analyze_end_time | 23:59 +0000 |
| tidb_auto_analyze_ratio | 0.5 |
| tidb_auto_analyze_start_time | 00:00 +0000 |
| tidb_backoff_lock_fast | 100 |
| tidb_backoff_weight | 2 |
| tidb_batch_commit | 0 |
| tidb_batch_delete | 0 |
| tidb_batch_insert | 0 |
| tidb_build_stats_concurrency | 4 |
| tidb_capture_plan_baselines | off |
| tidb_check_mb4_value_in_utf8 | 1 |
| tidb_checksum_table_concurrency | 4 |
| tidb_config | |
| tidb_constraint_check_in_place | 0 |
| tidb_current_ts | 0 |
| tidb_ddl_error_count_limit | 512 |
| tidb_ddl_reorg_batch_size | 256 |
| tidb_ddl_reorg_priority | PRIORITY_LOW |
| tidb_ddl_reorg_worker_cnt | 4 |
| tidb_disable_txn_auto_retry | 1 |
| tidb_distsql_scan_concurrency | 15 |
| tidb_dml_batch_size | 20000 |
| tidb_enable_cascades_planner | 0 |
| tidb_enable_chunk_rpc | 1 |
| tidb_enable_collect_execution_info | 1 |
| tidb_enable_fast_analyze | 0 |
| tidb_enable_index_merge | 0 |
| tidb_enable_noop_functions | 0 |
| tidb_enable_radix_join | 0 |
| tidb_enable_slow_log | 1 |
| tidb_enable_stmt_summary | 1 |
| tidb_enable_streaming | 0 |
| tidb_enable_table_partition | on |
| tidb_enable_vectorized_expression | 1 |
| tidb_enable_window_function | 1 |
| tidb_evolve_plan_baselines | off |
| tidb_evolve_plan_task_end_time | 23:59 +0000 |
| tidb_evolve_plan_task_max_time | 600 |
| tidb_evolve_plan_task_start_time | 00:00 +0000 |
| tidb_expensive_query_time_threshold | 60 |
| tidb_force_priority | NO_PRIORITY |
| tidb_general_log | 0 |
| tidb_hash_join_concurrency | 5 |
| tidb_hashagg_final_concurrency | 4 |
| tidb_hashagg_partial_concurrency | 4 |
| tidb_index_join_batch_size | 25000 |
| tidb_index_lookup_concurrency | 4 |
| tidb_index_lookup_join_concurrency | 4 |
| tidb_index_lookup_size | 20000 |
| tidb_index_serial_scan_concurrency | 1 |
| tidb_init_chunk_size | 32 |
| tidb_isolation_read_engines | tikv, tiflash, tidb |
| tidb_low_resolution_tso | 0 |
| tidb_max_chunk_size | 1024 |
| tidb_max_delta_schema_count | 1024 |
| tidb_mem_quota_hashjoin | 34359738368 |
| tidb_mem_quota_indexlookupjoin | 34359738368 |
| tidb_mem_quota_indexlookupreader | 34359738368 |
| tidb_mem_quota_mergejoin | 34359738368 |
| tidb_mem_quota_nestedloopapply | 34359738368 |
| tidb_mem_quota_query | 1073741824 |
| tidb_mem_quota_sort | 34359738368 |
| tidb_mem_quota_topn | 34359738368 |
| tidb_metric_query_range_duration | 60 |
| tidb_metric_query_step | 60 |
| tidb_opt_agg_push_down | 0 |
| tidb_opt_concurrency_factor | 3 |
| tidb_opt_copcpu_factor | 3 |
| tidb_opt_correlation_exp_factor | 1 |
| tidb_opt_correlation_threshold | 0.9 |
| tidb_opt_cpu_factor | 3 |
| tidb_opt_desc_factor | 3 |
| tidb_opt_disk_factor | 1.5 |
| tidb_opt_distinct_agg_push_down | 0 |
| tidb_opt_insubq_to_join_and_agg | 1 |
| tidb_opt_join_reorder_threshold | 0 |
| tidb_opt_memory_factor | 0.001 |
| tidb_opt_network_factor | 1 |
| tidb_opt_scan_factor | 1.5 |
| tidb_opt_seek_factor | 20 |
| tidb_opt_write_row_id | 0 |
| tidb_optimizer_selectivity_level | 0 |
| tidb_pprof_sql_cpu | 0 |
| tidb_projection_concurrency | 4 |
| tidb_query_log_max_len | 4096 |
| tidb_record_plan_in_slow_log | 1 |
| tidb_replica_read | leader |
| tidb_retry_limit | 10 |
| tidb_row_format_version | 2 |
| tidb_scatter_region | 0 |
| tidb_skip_isolation_level_check | 0 |
| tidb_skip_utf8_check | 0 |
| tidb_slow_log_threshold | 300 |
| tidb_slow_query_file | tidb-slow.log |
| tidb_snapshot | |
| tidb_stmt_summary_history_size | 24 |
| tidb_stmt_summary_internal_query | 0 |
| tidb_stmt_summary_max_sql_length | 4096 |
| tidb_stmt_summary_max_stmt_count | 200 |
| tidb_stmt_summary_refresh_interval | 1800 |
| tidb_store_limit | 0 |
| tidb_txn_mode | |
| tidb_use_plan_baselines | on |
| tidb_wait_split_region_finish | 1 |
| tidb_wait_split_region_timeout | 300 |
| tidb_window_concurrency | 4 |
+-------------------------------------+---------------------+
108 rows in set (0.01 sec)

mysql> SHOW GLOBAL VARIABLES LIKE 'time_zone%';
+---------------+--------+
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