如何检查MySQL数据库是否存在？

2023-06-21 03:47:03 451

schema_name命令用于检查MySQL数据库是否存在。此命令的语法如下-

select schema_name from information_schema.schemata where schema_name = 'database
name';

现在，上面的命令用于检查数据库是否存在。查询如下-

案例1-数据库存在。

mysql> select schema_name from information_schema.schemata where schema_name = 'business';

获得的输出如下-

+-------------+
| SCHEMA_NAME |
+-------------+
| business    |
+-------------+
1 row in set (0.00 sec)

案例2-数据库不存在。

mysql> select schema_name from information_schema.schemata where schema_name = 'sample2';
Empty set (0.00 sec)

Note: We can check how many databases are present in MySQL with the help of the show
command.

show命令的语法如下-

show databases;

使用上述语法的查询如下-

mysql> show databases;

以下是输出

+--------------------+
| Database           |
+--------------------+
| business           |
| hello              |
| information_schema |
| mybusiness         |
| mysql              |
| performance_schema |
| sample             |
| sys                |
| test               |
+--------------------+
9 rows in set (0.00 sec)

现在，我们可以在use命令的帮助下选择特定数据库的名称。查询如下-

mysql> use business;
Database changed

我们还可以检查特定数据库中存在的表数。这可以使用show命令来完成。对此的查询如下-

mysql> show tables;

执行上述查询后，获得以下输出-

+----------------------+
| Tables_in_business   |
+----------------------+
| addcolumntable       |
| bookindexes          |
| chardemo             |
| demo                 |
| demoascii            |
| demobcrypt           |
| demoint              |
| demoschema           |
| duplicatebookindexes |
| existsrowdemo        |
| foreigntable         |
| groupdemo            |
| int1demo             |
| intdemo              |
| latandlangdemo       |
| modifycolumnnamedemo |
| modifydatatype       |
| moviecollection      |
| mytable              |
| nthrecorddemo        |
| nulldemo             |
| primarytable         |
| primarytable1        |
| smallintdemo         |
| student              |
| tblstudent           |
| tbluni               |
| textdemo             |
| texturl              |
| varchardemo          |
| varcharurl           |
+----------------------+
31 rows in set (0.00 sec)

可以在desc命令的帮助下描述特定的表。其语法如下-

desc yourTableName;

现在，上面的语法用于描述表。对此的查询是-

mysql> desc modifydatatype;

以下是获得的输出-

+----------+--------------+------+-----+---------+-------+
| Field    | Type         | Null | Key | Default | Extra |
+----------+--------------+------+-----+---------+-------+
| id       | int(11)      | YES   |    | NULL    |       |
| YourName | varchar(100) | YES   |    | NULL    |       |
+----------+--------------+------+-----+---------+-------+
2 rows in set (0.00 sec)

如何检查MySQL数据库是否存在？

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