SQL 基础操作（MySQL 模式） | OceanBase 文档中心

本节主要介绍 OceanBase 数据库 MySQL 模式下的一些 SQL 基本操作。

创建数据库

使用 CREATE DATABASE 语句创建数据库。

示例：创建数据库 db1，指定字符集为 UTF8 ，并创建读写属性。

obclient> CREATE DATABASE db1 DEFAULT CHARACTER SET UTF8 READ WRITE;
Query OK, 1 row affected

表操作

本节主要提供数据库中表的创建、查看、修改和删除的语法和示例。

创建表

使用 CREATE TABLE 语句在数据库中创建新表。

示例：在数据库 db1 中创建表 test。

obclient> USE db1;
Database changed

obclient> CREATE TABLE test (c1 INT PRIMARY KEY, c2 VARCHAR(3));
Query OK, 0 rows affected

查看表

使用 SHOW CREATE TABLE 语句查看建表语句。

示例：查看表 test 的建表语句。

obclient> SHOW CREATE TABLE test\G
*************************** 1. row ***************************
       Table: test
Create Table: CREATE TABLE `test` (
  `c1` int(11) NOT NULL,
  `c2` varchar(3) DEFAULT NULL,
  PRIMARY KEY (`c1`)
) DEFAULT CHARSET = utf8mb4 ROW_FORMAT = DYNAMIC COMPRESSION = 'zstd_1.3.8' REPLICA_NUM = 1 BLOCK_SIZE = 16384 USE_BLOOM_FILTER = FALSE TABLET_SIZE = 134217728 PCTFREE = 0
1 row in set

使用 SHOW TABLES 语句查看指定数据库中的所有表。

示例：查看数据库 db1 中的所有表。

obclient> SHOW TABLES FROM db1;
+---------------+
| Tables_in_db1 |
+---------------+
| test          |
+---------------+
1 row in set

修改表

使用 ALTER TABLE 语句来修改已存在的表的结构，包括修改表及表属性、新增列、修改列及属性、删除列等。

示例 1：将表 test 的字段 c2 改名为 c3，并同时修改其字段类型。

obclient> DESCRIBE test;
+-------+------------+------+-----+---------+-------+
| Field | Type       | Null | Key | Default | Extra |
+-------+------------+------+-----+---------+-------+
| c1    | int(11)    | NO   | PRI | NULL    |       |
| c2    | varchar(3) | YES  |     | NULL    |       |
+-------+------------+------+-----+---------+-------+
2 rows in set

obclient> ALTER TABLE test CHANGE COLUMN c2 c3 CHAR(10);
Query OK, 0 rows affected

obclient> DESCRIBE test;
+-------+----------+------+-----+---------+-------+
| Field | Type     | Null | Key | Default | Extra |
+-------+----------+------+-----+---------+-------+
| c1    | int(11)  | NO   | PRI | NULL    |       |
| c3    | char(10) | YES  |     | NULL    |       |
+-------+----------+------+-----+---------+-------+
2 rows in set

示例 2：在表 test 中增加、删除列。

obclient> DESCRIBE test;
+-------+-------------+------+-----+---------+-------+
| Field | Type        | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| c1    | int(11)     | NO   | PRI | NULL    |       |
| c2    | varchar(3)  | YES  |     | NULL    |       |
+-------+-------------+------+-----+---------+-------+
2 rows in set

obclient> ALTER TABLE test ADD c3 int;
Query OK, 0 rows affected

obclient> DESCRIBE test;
+-------+-------------+------+-----+---------+-------+
| Field | Type        | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| c1    | int(11)     | NO   | PRI | NULL    |       |
| c2    | varchar(3)  | YES  |     | NULL    |       |
| c3    | int(11)     | YES  |     | NULL    |       |
+-------+-------------+------+-----+---------+-------+
3 rows in set

obclient> ALTER TABLE test DROP c3;
Query OK, 0 rows affected

obclient> DESCRIBE test;
+-------+-------------+------+-----+---------+-------+
| Field | Type        | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| c1    | int(11)     | NO   | PRI | NULL    |       |
| c2    | varchar(3)  | YES  |     | NULL    |       |
+-------+-------------+------+-----+---------+-------+
2 rows in set

删除表

使用 DROP TABLE 语句删除表。

示例：删除表 test。

obclient> DROP TABLE test;
Query OK, 0 rows affected

索引操作

索引是创建在表上并对数据库表中一列或多列的值进行排序的一种结构。其作用主要在于提高查询的速度，降低数据库系统的性能开销。

创建索引

使用 CREATE INDEX 语句创建表的索引。

示例：在表 test 中创建索引。

obclient> DESCRIBE test;
+-------+----------+------+-----+---------+-------+
| Field | Type     | Null | Key | Default | Extra |
+-------+----------+------+-----+---------+-------+
| c1    | int(11)  | NO   | PRI | NULL    |       |
| c3    | char(10) | YES  |     | NULL    |       |
+-------+----------+------+-----+---------+-------+
2 rows in set

obclient> CREATE INDEX test_index ON test (c1, c3);
Query OK, 0 rows affected

查看索引

使用 SHOW INDEX 语句查看表的索引。

示例：查看表 test 中的索引信息。

obclient> SHOW INDEX FROM test\G
*************************** 1. row ***************************
        Table: test
   Non_unique: 0
     Key_name: PRIMARY
 Seq_in_index: 1
  Column_name: c1
    Collation: A
  Cardinality: NULL
     Sub_part: NULL
       Packed: NULL
         Null:
   Index_type: BTREE
      Comment: available
Index_comment:
      Visible: YES
*************************** 2. row ***************************
        Table: test
   Non_unique: 1
     Key_name: test_index
 Seq_in_index: 1
  Column_name: c1
    Collation: A
  Cardinality: NULL
     Sub_part: NULL
       Packed: NULL
         Null:
   Index_type: BTREE
      Comment: available
Index_comment:
      Visible: YES
*************************** 3. row ***************************
        Table: test
   Non_unique: 1
     Key_name: test_index
 Seq_in_index: 2
  Column_name: c3
    Collation: A
  Cardinality: NULL
     Sub_part: NULL
       Packed: NULL
         Null: YES
   Index_type: BTREE
      Comment: available
Index_comment:
      Visible: YES
3 rows in set

删除索引

使用 DROP INDEX 语句删除表的索引。

示例：删除表 test 中的索引。

obclient> DROP INDEX test_index ON test;
Query OK, 0 rows affected

插入数据

使用 INSERT 语句在已经存在的表中插入数据。

示例 1：创建表 t1 并插入一行数据。

obclient> CREATE TABLE t1(c1 INT PRIMARY KEY, c2 int) PARTITION BY KEY(c1) PARTITIONS 4;
Query OK, 0 rows affected

obclient> SELECT * FROM t1;
Empty set

obclient> INSERT t1 VALUES(1,1);
Query OK, 1 row affected

obclient> SELECT * FROM t1;
+----+------+
| c1 | c2   |
+----+------+
|  1 |    1 |
+----+------+
1 row in set

示例 2：向表 t1 中插入多行数据。

obclient> INSERT t1 VALUES(2,2),(3,default),(2+2,3*4);
Query OK, 3 rows affected
Records: 3  Duplicates: 0  Warnings: 0

obclient> SELECT * FROM t1;
+----+------+
| c1 | c2   |
+----+------+
|  1 |    1 |
|  2 |    2 |
|  3 | NULL |
|  4 |   12 |
+----+------+
4 rows in set

删除数据

使用 DELETE 语句删除数据，支持单表删除和多表删除数据。

示例 1：通过 CREATE TABLE 创建表 t2 和 t3。删除 c1=2 的行，其中 c1 列为表 t2 中的 PRIMARY KEY。

/*表 `t3` 为 `KEY` 分区表，且分区名由系统根据分区命令规则自动生成，即分区名为 `p0`、`p1`、`p2`、`p3`*/
obclient> CREATE TABLE t2(c1 INT PRIMARY KEY, c2 INT);
Query OK, 0 rows affected

obclient> INSERT t2 VALUES(1,1),(2,2),(3,3),(4,4);
Query OK, 4 rows affected
Records: 4  Duplicates: 0  Warnings: 0

obclient> SELECT * FROM t2; 
+----+------+
| c1 | c2   |
+----+------+
|  1 |    1 |
|  2 |    2 |
|  3 |    3 |
|  4 |    4 |
+----+------+
4 rows in set

obclient> CREATE TABLE t3(c1 INT PRIMARY KEY, c2 INT) PARTITION BY KEY(c1) PARTITIONS 4;
Query OK, 0 rows affected

obclient> INSERT INTO t3 VALUES(5,5),(1,1),(2,2),(3,3);
Query OK, 4 rows affected
Records: 4  Duplicates: 0  Warnings: 0

obclient> SELECT * FROM t3;
+----+------+
| c1 | c2   |
+----+------+
|  5 |    5 |
|  1 |    1 |
|  2 |    2 |
|  3 |    3 |
+----+------+
4 rows in set

obclient> DELETE FROM t2 WHERE c1 = 2;
Query OK, 1 row affected

obclient> SELECT * FROM t2;
+----+------+
| c1 | c2   |
+----+------+
|  1 |    1 |
|  3 |    3 |
|  4 |    4 |
+----+------+
3 rows in set

示例 2：删除表 t2 中按照 c2 列排序之后的第一行数据。

obclient> DELETE FROM t2 ORDER BY c2 LIMIT 1;
Query OK, 1 row affected

obclient> SELECT * FROM t2;
+----+------+
| c1 | c2   |
+----+------+
|  3 |    3 |
|  4 |    4 |
+----+------+
2 rows in set

示例 3：删除表 t3 的 p2 分区的数据。

obclient> SELECT * FROM t3 PARTITION(p2); 
+----+------+
| c1 | c2   |
+----+------+
|  1 |    1 |
|  2 |    2 |
|  3 |    3 |
+----+------+
3 rows in set

obclient> DELETE FROM t3 PARTITION(p2); 
Query OK, 3 rows affected

obclient> SELECT * FROM t3;
+----+------+
| c1 | c2   | 
+----+------+
|  5 |    5 |
+----+------+
1 row in set

示例 4：删除 t2、t3 表中 t2.c1 = t3.c1 的数据。

obclient> SELECT * FROM t2;
+----+------+
| c1 | c2   |
+----+------+
|  3 |    3 |
|  5 |    5 |
+----+------+
2 rows in set

obclient> SELECT * FROM t3;
+----+------+
| c1 | c2   |
+----+------+ 
|  5 |    5 | 
+----+------+
1 row in set

obclient> DELETE t2, t3 FROM t2, t3 WHERE t2.c1 = t3.c1;
Query OK, 3 rows affected
/*等价于：
obclient> DELETE FROM t2, t3 USING t2, t3 WHERE t2.c1 = t3.c1;
*/

obclient> SELECT * FROM t2;
+----+------+
| c1 | c2   |
+----+------+
|  3 |    3 |
+----+------+
1 row in set

obclient> SELECT * FROM t3;
Empty set

更新数据

使用 UPDATE 语句修改表中的字段值。

示例 1：通过 CREATE TABLE 创建表 t4 和 t5，将表 t4 中 t2.c1=10 对应的那一行数据的 c2 列值修改为 100。

obclient> CREATE TABLE t4(c1 INT PRIMARY KEY, c2 INT);
Query OK, 0 rows affected

obclient> INSERT t4 VALUES(10,10),(20,20),(30,30),(40,40);
Query OK, 4 rows affected
Records: 4  Duplicates: 0  Warnings: 0

obclient> SELECT * FROM t4;
+----+------+
| c1 | c2   |
+----+------+
| 10 |   10 |
| 20 |   20 |
| 30 |   30 |
| 40 |   40 |
+----+------+
4 rows in set

obclient> CREATE TABLE t5(c1 INT PRIMARY KEY, c2 INT) PARTITION BY KEY(c1) PARTITIONS 4;
Query OK, 0 rows affected

obclient> INSERT t5 VALUES(50,50),(10,10),(20,20),(30,30);
Query OK, 4 rows affected
Records: 4  Duplicates: 0  Warnings: 0

obclient> SELECT * FROM t5;
+----+------+
| c1 | c2   |
+----+------+
| 20 |   20 |
| 10 |   10 |
| 50 |   50 |
| 30 |   30 |
+----+------+
4 rows in set

obclient> UPDATE t4 SET t4.c2 = 100 WHERE t4.c1 = 10;
Query OK, 1 row affected
Rows matched: 1  Changed: 1  Warnings: 0

obclient> SELECT * FROM t4;
+----+------+
| c1 | c2   |
+----+------+
| 10 |  100 |
| 20 |   20 |
| 30 |   30 |
| 40 |   40 |
+----+------+
4 rows in set

示例 2：将表 t4 中按照 c2 列排序的前两行数据的 c2 列值修改为 100。

obclient> UPDATE t4 set t4.c2 = 100 ORDER BY c2 LIMIT 2;
Query OK, 2 rows affected
Rows matched: 2  Changed: 2  Warnings: 0

obclient> SELECT * FROM t4;
+----+------+
| c1 | c2   |
+----+------+
| 10 |  100 |
| 20 |  100 |
| 30 |  100 |
| 40 |   40 |
+----+------+
4 rows in set

示例 3：将表 t5 中 p1 分区的数据中 t5.c1 > 20 的对应行数据的 c2 列值修改为 100。

obclient> SELECT * FROM t5 PARTITION (p1);
+----+------+
| c1 | c2   |
+----+------+
| 10 |   10 |
| 50 |   50 |
+----+------+
2 rows in set

obclient> UPDATE t5 PARTITION(p1) SET t5.c2 = 100 WHERE t5.c1 > 20;
Query OK, 1 row affected
Rows matched: 1  Changed: 1  Warnings: 0

obclient> SELECT * FROM t5 PARTITION(p1);
+----+------+
| c1 | c2   |
+----+------+
| 10 |   10 |
| 50 |  100 |
+----+------+
2 rows in set

示例 4：对于表 t4 和表 t5 中满足 t4.c2 = t5.c2 对应行的数据，将表 t4 中的 c2 列值修改为 100，表 t5 中的 c2 列值修改为 200。

obclient> UPDATE t4,t5 SET t4.c2 = 100, t5.c2 = 200 WHERE t4.c2 = t5.c2;
Query OK, 1 row affected 
Rows matched: 4  Changed: 1  Warnings: 0

obclient> SELECT * FROM t4;
+----+------+
| c1 | c2   |
+----+------+
| 10 |  100 |
| 20 |  100 |
| 30 |  100 |
| 40 |   40 |
+----+------+
4 rows in set

obclient> SELECT * FROM t5;
+----+------+
| c1 | c2   |
+----+------+
| 20 |   20 |
| 10 |   10 |
| 50 |  200 |
| 30 |   30 |
+----+------+
4 rows in set

查询数据

使用 SELECT 语句查询表中的内容。

示例 1：通过 CREATE TABLE 创建表 t6。从表 t6 中读取 name 的数据。

obclient> CREATE TABLE t6 (id INT, name VARCHAR(50), num INT);
Query OK, 0 rows affected

obclient> INSERT INTO t6 VALUES(1,'a',100),(2,'b',200),(3,'a',50);
Query OK, 3 rows affected
Records: 3  Duplicates: 0  Warnings: 0

obclient> SELECT * FROM t6;
+------+------+------+
| ID   | NAME | NUM  |
+------+------+------+
|    1 | a    |  100 |
|    2 | b    |  200 |
|    3 | a    |   50 |
+------+------+------+
3 rows in set

obclient> SELECT name FROM t6;
+------+
| NAME |
+------+
| a    |
| b    |
| a    |
+------+
3 rows in set

示例 2：在查询结果中对 name 进行去重处理。

obclient> SELECT DISTINCT name FROM t6;
+------+
| NAME |
+------+
| a    |
| b    |
+------+
2 rows in set

示例 3：从表 t6 中根据筛选条件 name = 'a' ，输出对应的 id 、name 和 num。

obclient> SELECT id, name, num FROM t6 WHERE name = 'a';
+------+------+------+
| ID   | NAME | NUM  |
+------+------+------+
|    1 | a    |  100 |
|    3 | a    |   50 |
+------+------+------+
2 rows in set

提交事务

使用 COMMIT 语句提交事务。

在您提交事务之前，您的修改只对当前会话可见，对其他数据库会话是不可见的；您的修改没有持久化，可以用 ROLLBACK 语句撤销修改。

在您提交事务之后，您的修改对所有数据库会话可见。您的修改结果持久化成功，不可以用 ROLLBACK 语句回滚修改。

示例：通过 CREATE TABLE 创建表 t_insert。使用 COMMIT 语句提交事务。

obclient> CREATE TABLE t_insert(
    id number NOT NULL PRIMARY KEY,
    name varchar(10) NOT NULL, 
    value number,
    gmt_create DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP
 );
Query OK, 0 rows affected

obclient> BEGIN;
Query OK, 0 rows affected

obclient> INSERT INTO t_insert(id, name, value, gmt_create) VALUES(1,'CN',10001, current_timestamp),(2,'US',10002, current_timestamp),(3,'EN',10003, current_timestamp);
Query OK, 3 rows affected
Records: 3  Duplicates: 0  Warnings: 0

obclient> SELECT * FROM t_insert;
+----+------+-------+---------------------+
| id | name | value | gmt_create          |
+----+------+-------+---------------------+
|  1 | CN   | 10001 | 2022-08-22 16:19:26 |
|  2 | US   | 10002 | 2022-08-22 16:19:26 |
|  3 | EN   | 10003 | 2022-08-22 16:19:26 |
+----+------+-------+---------------------+
3 rows in set

obclient> INSERT INTO t_insert(id,name) VALUES(4,'JP');
Query OK, 1 row affected

obclient> COMMIT;
Query OK, 0 rows affected

obclient> SELECT * FROM t_insert;
+----+------+-------+---------------------+
| id | name | value | gmt_create          |
+----+------+-------+---------------------+
|  1 | CN   | 10001 | 2022-08-22 16:19:26 |
|  2 | US   | 10002 | 2022-08-22 16:19:26 |
|  3 | EN   | 10003 | 2022-08-22 16:19:26 |
|  4 | JP   |  NULL | 2022-08-22 16:21:39 |
+----+------+-------+---------------------+
4 rows in set

回滚事务

使用 ROLLBACK 语句回滚事务。

回滚一个事务指将事务的修改全部撤销。可以回滚当前整个未提交的事务，也可以回滚到事务中任意一个保存点。如果要回滚到某个保存点，必须结合使用 ROLLBACK 和 TO SAVEPOINT 语句。其中：

如果回滚整个事务，则：
- 事务会结束
- 所有的修改会被丢弃
- 清除所有保存点
- 释放事务持有的所有锁
如果回滚到某个保存点，则：
- 事务不会结束
- 保存点之前的修改被保留，保存点之后的修改被丢弃
- 清除保存点之后的保存点（不包括保存点自身）
- 释放保存点之后事务持有的所有锁

示例：回滚事务的全部修改。

obclient> SELECT * FROM t_insert;
+----+------+-------+---------------------+
| id | name | value | gmt_create          |
+----+------+-------+---------------------+
|  1 | CN   | 10001 | 2022-08-22 16:19:26 |
|  2 | US   | 10002 | 2022-08-22 16:19:26 |
|  3 | EN   | 10003 | 2022-08-22 16:19:26 |
+----+------+-------+---------------------+
3 rows in set

obclient> BEGIN;
Query OK, 0 rows affected

obclient> INSERT INTO t_insert(id, name, value) VALUES(4,'JP',10004),(5,'FR',10005),(6,'RU',10006);
Query OK, 3 rows affected
Records: 3  Duplicates: 0  Warnings: 0

obclient> SELECT * FROM t_insert;
+----+------+-------+---------------------+
| id | name | value | gmt_create          |
+----+------+-------+---------------------+
|  1 | CN   | 10001 | 2022-08-22 16:19:26 |
|  2 | US   | 10002 | 2022-08-22 16:19:26 |
|  3 | EN   | 10003 | 2022-08-22 16:19:26 |
|  4 | JP   | 10004 | 2022-08-22 16:26:23 |
|  5 | FR   | 10005 | 2022-08-22 16:26:23 |
|  6 | RU   | 10006 | 2022-08-22 16:26:23 |
+----+------+-------+---------------------+
6 rows in set

obclient> ROLLBACK;
Query OK, 0 rows affected

obclient> SELECT * FROM t_insert;
+----+------+-------+---------------------+
| id | name | value | gmt_create          |
+----+------+-------+---------------------+
|  1 | CN   | 10001 | 2022-08-22 16:19:26 |
|  2 | US   | 10002 | 2022-08-22 16:19:26 |
|  3 | EN   | 10003 | 2022-08-22 16:19:26 |
+----+------+-------+---------------------+
3 rows in set