2 rows in set (0.00 sec) 1. 2. 3. 4. 5. 6. 7. 某些情况下,子查询可以转化为表连接,例如:mysql> select * from emp where deptno in(select deptno from dept); +---+---+---+---+ | ename | hiredate | sal | deptno | +---+---+---+---+ | zzx | 2000-01-01 | 2000....
事务是一个整体,由一条或者多条SQL语句组成,这些SQL语句要么都执行成功,要么就失败,只要有一条SQL出现异常,整个操作就会回滚。回滚: 就是事务运行的过程中发生了某种故障,或者SQL出现了异常,事务不能继续执行,系统将事务中对数据库的所有已完成的操作全部取消,回滚到事务开始时的状态。
| Grant option | Databases,Tables,Functions,Procedures | To give to other users those privileges you possess | | Index | Tables | To create or drop indexes | | Insert | Tables | To insert data into tables | | Lock tables | Databases | To use LOCK TABLES (together with SELECT privilege...
4 rows in set (0.00 sec) 注意:子查询和表连接之间的转换主要应用在两个方面:MySQL 4.1 以前的版本不支持子查询,需要用表连接来实现子查询的功能 表连接在很多情况下用于优化子查询 (7)记录联合。 我们经常会碰到这样的应用,将两个表的数据按照一定的查询条件查询出来后,将结果合并到一起显示出来,这个时候,就...
GRANT { EXECUTE | ALL [ PRIVILEGES ] } ON { FUNCTION {function_name ( [ {[ argmode ] [ arg_name ] arg_type} [, ...] ] )} [, ...] | ALL FUNCTIONS IN SCHEMA schema_name [, ...] } TO { [ GROUP ] role_name | PUBLIC } [, ...] [ WITH GRANT OPTION ]; 将过程语...
SQL Reference GaussDB SQL Keywords Data Types Character Sets and Collations Constant and Macro Functions and Operators Expressions Pseudocolumn Type Conversion System Operation Controlling Transactions SQL Syntax SQL Syntax DCL Syntax Overview DDL Syntax Overview DML Syntax Overview Other Syntax List A B C...
Avoid using functions in predicates AND, OR, NOT operator should be avoided Use WHERE clause instead of HAVING Q.4: What is DDL in SQL? The SQL commands that can be used to describe the database structure are collectively known as Data Definition Language. It simply works with database sch...
GROUP BY Clause: Used with aggregate functions (like COUNT, MAX, MIN, SUM, AVG) to group the result set by one or more columns. Syntax:SELECT column1, aggregate_function(column2) FROM table_name GROUP BY column1; ORDER BY Clause: Used to sort the result set in ascending or descending...
REVOKE [ GRANT OPTION FOR ] { EXECUTE | ALL [ PRIVILEGES ] } ON { FUNCTION {function_name ( [ {[ argmode ] [ arg_name ] arg_type} [, ...] ] )} [, ...] | ALL FUNCTIONS IN SCHEMA schema_name [, ...] } FROM { [ GROUP ] role_name | PUBLIC } [, ...] [ CASCADE...
In a production environment, the database typically runs on a fileserver or networked personal computer and is used by many users. The database administrator (DBA) normally assigns user IDs, which are the heart of SQL security. As is the case for the single-user environment, each user ID ...