USE 语句

用于设置会话的当前数据库。

语法

USE db

如果查询语句中没有在表名前面以加点的方式指明数据库名，则用当前数据库进行搜索。

使用 HTTP 协议时无法进行此查询，因为没有会话的概念。

db > show databases;
+-----------+
| Databases |
| db        |
| db1       |
| db2       |
| system    |
+-----------+

Total: 4, Elapsed: 201.374917ms

db > use db;
db > show tables;
+--------------+---------------------+-----------------+--------------+---------------+---------------+
| TABLE_SCHEMA |     TABLE_NAME      | TABLE_METATABLE | TABLE_KEYCOL | TABLE_TIMECOL | TABLE_OPTIONS |
|     db       | kudu_gb32960_extend |     false       |     vin      |   e_t_date    |     null      |
|     db       |     kudu_all_type   |     false       |     vin      |   e_t_date    |     null      |
|     db       |        dsadsa       |     false       |      b       |      c        |     null      |
+--------------+---------------------+-----------------+--------------+---------------+---------------+

Total: 3, Elapsed: 203.320453ms

db > select vin from kudu_gb32960_extend limit 1;
+-------------------+
| vin(VtString)     |
| LJNEDV1T5JN650697 |
+-------------------+

Total: 1, Elapsed: 205.602085ms

db > use db2;
db2 > show tables;
+--------------+--------------+-----------------+--------------+---------------+---------------+
| TABLE_SCHEMA |  TABLE_NAME  | TABLE_METATABLE | TABLE_KEYCOL | TABLE_TIMECOL | TABLE_OPTIONS |
|     db2      |    test      |     false       |     name     |    birth      | null          |
|     db2      | vehicle_info |     true        |              |  create_time  | null          |
+--------------+--------------+-----------------+--------------+---------------+---------------+

Total: 2, Elapsed: 202.62853ms

db2 > select vin from vehicle_info limit 1;
+-------------------+
| vin(VtString)     |
| LS5A2AJX8GA005478 |
+-------------------+

Total: 1, Elapsed: 234.167322ms

db2 > select vin from kudu_gb32960_extend limit 1;
error: ErrCode: -4, err: generate select query failed, sql:select vin from kudu_gb32960_extend limit 1, err:Table 'db2.kudu_gb32960_extend' doesn't exist

db2 > select vin from db.kudu_gb32960_extend limit 1;
+-------------------+
| vin(VtString)     |
| LJNEDV1T5JN650697 |
+-------------------+

Total: 1, Elapsed: 206.736874ms

db2 > use db;
db > select vin from vehicle_info limit 1;
error: ErrCode: -4, err: generate select query failed, sql:select vin from vehicle_info limit 1, err:Table 'db.vehicle_info' doesn't exist

db > select vin from db2.vehicle_info limit 1;
+-------------------+
| vin(VtString)     |
| LS5A2AJX8GA005478 |
+-------------------+

Total: 1, Elapsed: 239.052253ms

db > create database if not exists magus;
create success, elapsed: 22.036328ms

db > show databases;
+---------------------+
| Databases(VtString) |
| db                  |
| db1                 |
| db2                 |
| db3                 |
| magus               |
| system              |
+---------------------+

Total: 6, Elapsed: 201.672373ms

db > drop database if exists magus;
+---------------------+
| Databases(VtString) |
| db                  |
| db1                 |
| db2                 |
| db3                 |
| system              |
+---------------------+