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Capitalize sql keywords in several files #4862

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Nov 10, 2020
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Capitalize sql keywords in several files #4862

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31 changes: 15 additions & 16 deletions auto-random.md
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Expand Up @@ -17,29 +17,29 @@ aliases: ['/docs-cn/dev/auto-random/','/docs-cn/dev/reference/sql/attributes/aut
以下面语句建立的表为例：

```sql
create table t (a bigint primary key auto_increment, b varchar(255))
CREATE TABLE t (a bigint PRIMARY KEY AUTO_INCREMENT, b varchar(255))
```

在以上语句所建的表上执行大量未指定主键值的 `INSERT` 语句，示例如下：

```sql
insert into t(b) values ('a'), ('b'), ('c')
INSERT INTO t(b) VALUES ('a'), ('b'), ('c')
```

如以上语句，由于未指定主键列的值（`a` 列），TiDB 会使用连续自增的行值作为行 ID，可能导致单个 TiKV 节点上产生写入热点，进而影响对外提供服务的性能。要避免这种写入热点，可以在执行建表语句时为 `a` 列指定 `AUTO_RANDOM` 属性而不是 `AUTO_INCREMENT` 属性。示例如下：

{{< copyable "sql" >}}

```sql
create table t (a bigint primary key auto_random, b varchar(255))
CREATE TABLE t (a bigint PRIMARY KEY AUTO_RANDOM, b varchar(255))
```

或者

{{< copyable "sql" >}}

```sql
create table t (a bigint auto_random, b varchar(255), primary key (a))
CREATE TABLE t (a bigint AUTO_RANDOM, b varchar(255), PRIMARY KEY (a))
```

此时再执行形如 `INSERT INTO t(b) values...` 的 `INSERT` 语句。
Expand All @@ -60,7 +60,7 @@ create table t (a bigint auto_random, b varchar(255), primary key (a))
{{< copyable "sql" >}}

```sql
create table t (a bigint primary key auto_random(3), b varchar(255))
CREATE TABLE t (a bigint PRIMARY KEY AUTO_RANDOM(3), b varchar(255))
```

以上建表语句中，shard bits 的数量为 `3`。shard bits 的数量的取值范围是 `[1, field_max_bits)`，其中 `field_max_bits` 为整型主键列类型占用的位长度。
Expand All @@ -70,16 +70,15 @@ create table t (a bigint primary key auto_random(3), b varchar(255))
{{< copyable "sql" >}}

```sql
show warnings
SHOW WARNINGS
```

```
```sql
+-------+------+----------------------------------------------------------+
| Level | Code | Message |
+-------+------+----------------------------------------------------------+
| Note | 1105 | Available implicit allocation times: 1152921504606846976 |
+-------+------+----------------------------------------------------------+

```

> **注意：**
Expand All @@ -88,19 +87,19 @@ show warnings

另外，要查看某张含有 `AUTO_RANDOM` 属性的表的 shard bits 数量，可以在系统表 `information_schema.tables` 中 `TIDB_ROW_ID_SHARDING_INFO` 一列看到模式为 `PK_AUTO_RANDOM_BITS=x` 的值，其中 `x` 为 shard bits 的数量。

`AUTO RANDOM` 列隐式分配的值会影响 `last_insert_id()`。可以使用 `select last_insert_id()` 获取上一次 TiDB 隐式分配的 ID，例如：
`AUTO RANDOM` 列隐式分配的值会影响 `last_insert_id()`。可以使用 `SELECT last_insert_id()` 获取上一次 TiDB 隐式分配的 ID，例如：

{{< copyable "sql" >}}

```sql
insert into t (b) values ("b")
select * from t;
select last_insert_id()
INSERT INTO t (b) VALUES ("b")
SELECT * FROM t;
SELECT last_insert_id()
```

可能得到的结果如下：

```
```sql
+------------+---+
| a | b |
+------------+---+
Expand All @@ -121,18 +120,18 @@ TiDB 支持解析版本注释语法。示例如下：
{{< copyable "sql" >}}

```sql
create table t (a bigint primary key /*T![auto_rand] auto_random */)
CREATE TABLE t (a bigint PRIMARY KEY /*T![auto_rand] auto_random */)
```

{{< copyable "sql" >}}

```sql
create table t (a bigint primary key auto_random)
CREATE TABLE t (a bigint PRIMARY KEY AUTO_RANDOM)
```

以上两个语句含义相同。

在 `show create table` 的结果中，`AUTO_RANDOM` 属性会被注释掉。注释会附带一个特性标识符，例如 `/*T![auto_rand] auto_random */`。其中 `auto_rand` 表示 `AUTO_RANDOM` 的特性标识符，只有实现了该标识符对应特性的 TiDB 版本才能够正常解析 SQL 语句片段。
在 `SHOW CREATE TABLE` 的结果中，`AUTO_RANDOM` 属性会被注释掉。注释会附带一个特性标识符，例如 `/*T![auto_rand] auto_random */`。其中 `auto_rand` 表示 `AUTO_RANDOM` 的特性标识符，只有实现了该标识符对应特性的 TiDB 版本才能够正常解析 SQL 语句片段。

该功能支持向前兼容，即降级兼容。没有实现对应特性的 TiDB 版本则会忽略表（带有上述注释）的 `AUTO_RANDOM` 属性，因此能够使用含有该属性的表。

Expand Down
4 changes: 2 additions & 2 deletions backup-and-restore-using-dumpling-lightning.md
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Expand Up @@ -67,15 +67,15 @@ Could not read data from testSchema.testTable: GC life time is shorter than tran
{{< copyable "sql" >}}

```sql
update mysql.tidb set VARIABLE_VALUE = '720h' where VARIABLE_NAME = 'tikv_gc_life_time';
UPDATE mysql.tidb SET VARIABLE_VALUE = '720h' WHERE VARIABLE_NAME = 'tikv_gc_life_time';
```

2. 执行 `dumpling` 命令后，将 TiDB 集群的 GC 值恢复到第 1 步中的初始值：

{{< copyable "sql" >}}

```sql
update mysql.tidb set VARIABLE_VALUE = '10m' where VARIABLE_NAME = 'tikv_gc_life_time';
UPDATE mysql.tidb SET VARIABLE_VALUE = '10m' WHERE VARIABLE_NAME = 'tikv_gc_life_time';
```

## 向 TiDB 恢复数据
Expand Down
4 changes: 2 additions & 2 deletions backup-and-restore-using-mydumper-lightning.md
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Expand Up @@ -78,15 +78,15 @@ aliases: ['/docs-cn/dev/backup-and-restore-using-mydumper-lightning/','/docs-cn/
{{< copyable "sql" >}}

```sql
update mysql.tidb set VARIABLE_VALUE = '720h' where VARIABLE_NAME = 'tikv_gc_life_time';
UPDATE mysql.tidb SET VARIABLE_VALUE = '720h' WHERE VARIABLE_NAME = 'tikv_gc_life_time';
```

2. 执行 `mydumper` 命令后，将 TiDB 集群的 GC 值恢复到第 1 步中的初始值：

{{< copyable "sql" >}}

```sql
update mysql.tidb set VARIABLE_VALUE = '10m' where VARIABLE_NAME = 'tikv_gc_life_time';
UPDATE mysql.tidb SET VARIABLE_VALUE = '10m' WHERE VARIABLE_NAME = 'tikv_gc_life_time';
```

## 向 TiDB 恢复数据
Expand Down
8 changes: 4 additions & 4 deletions basic-sql-operations.md
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Expand Up @@ -40,7 +40,7 @@ SHOW DATABASES;
{{< copyable "sql" >}}

```sql
use mysql;
USE mysql;
```

使用 `SHOW TABLES` 语句查看数据库中的所有表。例如：
Expand Down Expand Up @@ -104,7 +104,7 @@ CREATE TABLE person (
{{< copyable "sql" >}}

```sql
SHOW CREATE table person;
SHOW CREATE TABLE person;
```

使用 `DROP TABLE` 语句删除表。例如：
Expand Down Expand Up @@ -154,7 +154,7 @@ ALTER TABLE person ADD UNIQUE person_unique_id (id);
{{< copyable "sql" >}}

```sql
SHOW INDEX from person;
SHOW INDEX FROM person;
```

使用 `ALTER TABLE` 或 `DROP INDEX` 语句来删除索引。与 `CREATE INDEX` 语句类似，`DROP INDEX` 也可以嵌入 `ALTER TABLE` 语句。例如：
Expand Down Expand Up @@ -241,7 +241,7 @@ SELECT name FROM person;
{{< copyable "sql" >}}

```sql
SELECT * FROM person where id<5;
SELECT * FROM person WHERE id<5;
```

常用的 DCL 功能是创建或删除用户，和对用户权限的管理。
Expand Down
28 changes: 14 additions & 14 deletions blacklist-control-plan.md
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Expand Up @@ -43,27 +43,27 @@ aliases: ['/docs-cn/dev/blacklist-control-plan/']
{{< copyable "sql" >}}

```sql
insert into mysql.opt_rule_blacklist values("join_reorder"), ("topn_push_down");
INSERT INTO mysql.opt_rule_blacklist VALUES("join_reorder"), ("topn_push_down");
```

执行以下 SQL 语句可让禁用规则立即生效，包括相应 TiDB Server 的所有旧链接：

{{< copyable "sql" >}}

```sql
admin reload opt_rule_blacklist;
ADMIN reload opt_rule_blacklist;
```

> **注意：**
>
>
> `admin reload opt_rule_blacklist` 只对执行该 SQL 语句的 TiDB server 生效。若需要集群中所有 TiDB server 生效，需要在每台 TiDB server 上执行该 SQL 语句。

- 需要解除一条规则的禁用时，需要删除表中禁用该条规则的相应数据，再执行 `admin reload`：

{{< copyable "sql" >}}

```sql
delete from mysql.opt_rule_blacklist where name in ("join_reorder", "topn_push_down");
DELETE FROM mysql.opt_rule_blacklist WHERE name IN ("join_reorder", "topn_push_down");
admin reload opt_rule_blacklist;
```

Expand All @@ -83,15 +83,15 @@ aliases: ['/docs-cn/dev/blacklist-control-plan/']
| [日期运算](/functions-and-operators/date-and-time-functions.md) | [`DATE_FORMAT()`](https://dev.mysql.com/doc/refman/5.7/en/date-and-time-functions.html#function_date-format) |

### 禁止特定表达式下推

当函数的计算过程由于下推而出现异常时，可通过黑名单功能禁止其下推来快速恢复业务。具体而言，你可以将上述支持的函数或运算符名加入黑名单 `mysql.expr_pushdown_blacklist` 中，以禁止特定表达式下推。

`mysql.expr_pushdown_blacklist` 的 schema 如下：

{{< copyable "sql" >}}

```sql
desc mysql.expr_pushdown_blacklist;
DESC mysql.expr_pushdown_blacklist;
```

```sql
Expand Down Expand Up @@ -147,7 +147,7 @@ desc mysql.expr_pushdown_blacklist;
{{< copyable "sql" >}}

```sql
explain select * from t where a < 2 and a > 2;
EXPLAIN SELECT * FROM t WHERE a < 2 AND a > 2;
```

```sql
Expand All @@ -166,7 +166,7 @@ desc mysql.expr_pushdown_blacklist;
{{< copyable "sql" >}}

```sql
insert into mysql.expr_pushdown_blacklist values('<','tikv',''), ('>','tikv','');
INSERT INTO mysql.expr_pushdown_blacklist VALUES('<','tikv',''), ('>','tikv','');
```

```sql
Expand All @@ -177,7 +177,7 @@ desc mysql.expr_pushdown_blacklist;
{{< copyable "sql" >}}

```sql
admin reload expr_pushdown_blacklist;
ADMIN reload expr_pushdown_blacklist;
```

```sql
Expand All @@ -189,7 +189,7 @@ desc mysql.expr_pushdown_blacklist;
{{< copyable "sql" >}}

```sql
explain select * from t where a < 2 and a > 2;
EXPLAIN SELECT * FROM t WHERE a < 2 and a > 2;
```

```sql
Expand All @@ -208,7 +208,7 @@ desc mysql.expr_pushdown_blacklist;
{{< copyable "sql" >}}

```sql
delete from mysql.expr_pushdown_blacklist where name = '>';
DELETE FROM mysql.expr_pushdown_blacklist WHERE name = '>';
```

```sql
Expand All @@ -218,7 +218,7 @@ desc mysql.expr_pushdown_blacklist;
{{< copyable "sql" >}}

```sql
admin reload expr_pushdown_blacklist;
ADMIN reload expr_pushdown_blacklist;
```

```sql
Expand All @@ -230,7 +230,7 @@ desc mysql.expr_pushdown_blacklist;
{{< copyable "sql" >}}

```sql
explain select * from t where a < 2 and a > 2;
EXPLAIN SELECT * FROM t WHERE a < 2 AND a > 2;
```

```sql
Expand Down
28 changes: 14 additions & 14 deletions character-set-and-collation.md
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Expand Up @@ -174,7 +174,7 @@ ALTER DATABASE db_name
{{< copyable "sql" >}}

```sql
create schema test1 character set utf8mb4 COLLATE uft8mb4_general_ci;
CREATE SCHEMA test1 CHARACTER SET utf8mb4 COLLATE uft8mb4_general_ci;
```

```sql
Expand All @@ -184,7 +184,7 @@ Query OK, 0 rows affected (0.09 sec)
{{< copyable "sql" >}}

```sql
use test1;
USE test1;
```

```sql
Expand All @@ -209,7 +209,7 @@ SELECT @@character_set_database, @@collation_database;
{{< copyable "sql" >}}

```sql
create schema test2 character set latin1 COLLATE latin1_bin;
CREATE SCHEMA test2 CHARACTER SET latin1 COLLATE latin1_bin;
```

```sql
Expand All @@ -219,7 +219,7 @@ Query OK, 0 rows affected (0.09 sec)
{{< copyable "sql" >}}

```sql
use test2;
USE test2;
```

```sql
Expand Down Expand Up @@ -390,13 +390,13 @@ SELECT _utf8mb4'string' COLLATE utf8mb4_general_ci;
{{< copyable "sql" >}}

```sql
create table t(a varchar(20) charset utf8mb4 collate utf8mb4_general_ci primary key);
CREATE TABLE t(a varchar(20) charset utf8mb4 collate utf8mb4_general_ci PRIMARY KEY);
Query OK, 0 rows affected
insert into t values ('A');
INSERT INTO t VALUES ('A');
Query OK, 1 row affected
insert into t values ('a');
INSERT INTO t VALUES ('a');
Query OK, 1 row affected # TiDB 会执行成功，而在 MySQL 中，则由于 utf8mb4_general_ci 大小写不敏感，报错 Duplicate entry 'a'。
insert into t1 values ('a ');
INSERT INTO t VALUES ('a ');
Query OK, 1 row affected # TiDB 会执行成功，而在 MySQL 中，则由于补齐空格比较，报错 Duplicate entry 'a '。
```

Expand All @@ -407,7 +407,7 @@ TiDB 4.0 新增了完整的排序规则支持框架，从语义上支持了排
{{< copyable "sql" >}}

```sql
select VARIABLE_VALUE from mysql.tidb where VARIABLE_NAME='new_collation_enabled';
SELECT VARIABLE_VALUE FROM mysql.tidb WHERE VARIABLE_NAME='new_collation_enabled';
```

```sql
Expand All @@ -426,13 +426,13 @@ select VARIABLE_VALUE from mysql.tidb where VARIABLE_NAME='new_collation_enabled
{{< copyable "sql" >}}

```sql
create table t(a varchar(20) charset utf8mb4 collate utf8mb4_general_ci primary key);
CREATE TABLE t(a varchar(20) charset utf8mb4 collate utf8mb4_general_ci PRIMARY KEY);
Query OK, 0 rows affected (0.00 sec)
insert into t values ('A');
INSERT INTO t VALUES ('A');
Query OK, 1 row affected (0.00 sec)
insert into t values ('a');
INSERT INTO t VALUES ('a');
ERROR 1062 (23000): Duplicate entry 'a' for key 'PRIMARY' # TiDB 兼容了 MySQL 的 case insensitive collation。
insert into t values ('a ');
INSERT INTO t VALUES ('a ');
ERROR 1062 (23000): Duplicate entry 'a ' for key 'PRIMARY' # TiDB 修正了 `PADDING` 行为，与 MySQL 兼容。
```

Expand Down Expand Up @@ -468,7 +468,7 @@ TiDB 支持使用 `COLLATE` 子句来指定一个表达式的排序规则，该
{{< copyable "sql" >}}

```sql
select 'a' = _utf8mb4 'A' collate utf8mb4_general_ci;
SELECT 'a' = _utf8mb4 'A' collate utf8mb4_general_ci;
```

```sql
Expand Down