dev/reference/sql: add sql statements

dev/reference/sql/statements/add-column.md

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+---
+title: ADD COLUMN
+summary: TiDB 数据库中 ADD COLUMN 的使用概况。
+category: reference
+---
+
+# ADD COLUMN 
+
+`ALTER TABLE.. ADD COLUMN` 语句用于在已有表中添加列。在 TiDB 中，`ADD COLUMN`为在线操作，不会影响表中的数据读写。
+
+## 总览
+
+**AlterTableStmt:**
+
+![AlterTableStmt](/media/sqlgram/AlterTableStmt.png)
+
+**AlterTableSpec:**
+
+![AlterTableSpec](/media/sqlgram/AlterTableSpec.png)
+
+**ColumnKeywordOpt:**
+
+![ColumnKeywordOpt](/media/sqlgram/ColumnKeywordOpt.png)
+
+**ColumnDef:**
+
+![ColumnDef](/media/sqlgram/ColumnDef.png)
+
+**ColumnPosition:**
+
+![ColumnPosition](/media/sqlgram/ColumnPosition.png)
+
+## 实例
+
+```sql
+mysql> CREATE TABLE t1 (id INT NOT NULL PRIMARY KEY auto_increment);
+Query OK, 0 rows affected (0.11 sec)
+
+mysql> INSERT INTO t1 VALUES (NULL);
+Query OK, 1 row affected (0.02 sec)
+
+mysql> SELECT * FROM t1;
++----+
+| id |
++----+
+|  1 |
++----+
+1 row in set (0.00 sec)
+
+mysql> ALTER TABLE t1 ADD COLUMN c1 INT NOT NULL;
+Query OK, 0 rows affected (0.28 sec)
+
+mysql> SELECT * FROM t1;
++----+----+
+| id | c1 |
++----+----+
+|  1 |  0 |
++----+----+
+1 row in set (0.00 sec)
+
+mysql> ALTER TABLE t1 ADD c2 INT NOT NULL AFTER c1;
+Query OK, 0 rows affected (0.28 sec)
+
+mysql> SELECT * FROM t1;
++----+----+----+
+| id | c1 | c2 |
++----+----+----+
+|  1 |  0 |  0 |
++----+----+----+
+1 row in set (0.00 sec)
+```
+
+## MySQL 兼容性
+
+* 不支持同时添加多列。
+* 不支持将新添加的列设为 `PRIMARY KEY`。
+* 不支持将新添加的列设为 `AUTO_INCREMENT`。
+
+## 另请参阅
+
+* [ADD INDEX](/dev/reference/sql/statements/add-index.md)
+* [CREATE TABLE](/dev/reference/sql/statements/create-table.md)

dev/reference/sql/statements/add-index.md

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+---
+title: ADD INDEX
+summary: TiDB 数据库中 ADD INDEX 的使用概况。
+category: reference
+---
+
+# ADD INDEX
+
+`ALTER TABLE.. ADD INDEX` 语句用于在已有表中添加一条索引。在 TiDB 中，`ADD INDEX` 为在线操作，不会影响表中的数据读写。
+
+## 总览
+
+**AlterTableStmt:**
+
+![AlterTableStmt](/media/sqlgram/AlterTableStmt.png)
+
+**AlterTableSpec:**
+
+![AlterTableSpec](/media/sqlgram/AlterTableSpec.png)
+
+**ColumnKeywordOpt:**
+
+![ColumnKeywordOpt](/media/sqlgram/ColumnKeywordOpt.png)
+
+**ColumnDef:**
+
+![ColumnDef](/media/sqlgram/ColumnDef.png)
+
+**ColumnPosition:**
+
+![ColumnPosition](/media/sqlgram/ColumnPosition.png)
+
+## 实例
+
+```sql
+mysql> CREATE TABLE t1 (id INT NOT NULL PRIMARY KEY auto_increment, c1 INT NOT NULL);
+Query OK, 0 rows affected (0.11 sec)
+
+mysql> INSERT INTO t1 (c1) VALUES (1),(2),(3),(4),(5);
+Query OK, 5 rows affected (0.03 sec)
+Records: 5  Duplicates: 0  Warnings: 0
+
+mysql> EXPLAIN SELECT * FROM t1 WHERE c1 = 3;
++---------------------+----------+------+-------------------------------------------------------------+
+| id                  | count    | task | operator info                                               |
++---------------------+----------+------+-------------------------------------------------------------+
+| TableReader_7       | 10.00    | root | data:Selection_6                                            |
+| └─Selection_6       | 10.00    | cop  | eq(test.t1.c1, 3)                                           |
+|   └─TableScan_5     | 10000.00 | cop  | table:t1, range:[-inf,+inf], keep order:false, stats:pseudo |
++---------------------+----------+------+-------------------------------------------------------------+
+3 rows in set (0.00 sec)
+
+mysql> ALTER TABLE t1 ADD INDEX (c1);
+Query OK, 0 rows affected (0.30 sec)
+
+mysql> EXPLAIN SELECT * FROM t1 WHERE c1 = 3;
++-------------------+-------+------+-----------------------------------------------------------------+
+| id                | count | task | operator info                                                   |
++-------------------+-------+------+-----------------------------------------------------------------+
+| IndexReader_6     | 10.00 | root | index:IndexScan_5                                               |
+| └─IndexScan_5     | 10.00 | cop  | table:t1, index:c1, range:[3,3], keep order:false, stats:pseudo |
++-------------------+-------+------+-----------------------------------------------------------------+
+2 rows in set (0.00 sec)
+```
+
+## MySQL 兼容性
+
+* 不支持 `FULLTEXT`，`HASH` 和 `SPATIAL` 索引。
+* 不支持降序索引（类似于 MySQL 5.7）。
+* 目前尚不支持同时添加多条索引。
+* 无法向表中添加 `PRIMARY KEY`。
+
+## 另请参阅
+
+* [CREATE INDEX](/dev/reference/sql/statements/create-index.md)
+* [DROP INDEX](/dev/reference/sql/statements/drop-index.md)
+* [RENAME INDEX](/dev/reference/sql/statements/rename-index.md)
+* [ADD COLUMN](/dev/reference/sql/statements/add-column.md)
+* [CREATE TABLE](/dev/reference/sql/statements/create-table.md)
+* [EXPLAIN](/dev/reference/sql/statements/explain.md)