IF NOT EXISTS是一个条件语句,在SQL中主要用于在尝试执行某个操作(如创建表、视图等)之前,检查该对象是否已经存在。这样做可以避免因尝试重复创建已存在的对象而导致的错误。然而,需要注意的是,IF NOT EXISTS并不直接支持所有SQL语句,特别是在修改表结构时(如ALTER TABLE)。 3. 说明为何ALTER TABLE IF NOT EXISTS...
ALTER TABLE 表名 ADD COLUMN IF NOT EXISTS 列名 列数据类型 DEFAULT 默认值; IF NOT EXISTS这个参数用法就是让查询时若该列不存在,则自动添加,若存在则什么也不做。因此,运用此语句能够达到自动添加列的目的。 一个具体的例子如下所示: ALTER TABLE user ADD COLUMN IF NOT EXISTS mobile VARCHAR(50) DEFAUL...
Note that the rarely usedALTER COLUMNsyntax has not anIF EXISTSoption, so the longerMODIFYsyntax must be used instead. Also note that the PostgreSQL syntax isnotsupported; thus, this willnotwork: ALTER TABLE IF EXISTS tab_name ... ; At this point, you are probably wondering: “But then,...
dbtype: mariadb dbversion: 11.2.3 druid verion: 1.2.20 error sql: alter table info_course drop column if exists course_type_id testcase code: stacktrace info: 21:53:17.933 [main] ERROR c.a.d.f.s.StatFilter - [mergeSql,150] - merge sql er...
[ IF EXISTS ] name DETACH PARTITION partition_name 其中action 是以下之一: ADD [ COLUMN ] [ IF NOT EXISTS ] column_name data_type [ COLLATE collation ] [ column_constraint [ ... ] ] DROP [ COLUMN ] [ IF EXISTS ] column_name [ RESTRICT | CASCADE ] ALTER [ COLUMN ] column_name [...
1 CREATE DATABASE 句法 2 3 CREATE DATABASE [IF NOT EXISTS] db_name 4 5 CREATE DATABASE 以给定名字创建一个数据库。允许的数据库名规则在章节 6.1.2 数据库、表、索引、列和别名 中被给出。 如果数据库已经存在,并且你...
CREATE [TEMPORARY] TABLE [IF NOT EXISTS] tbl_name [(create_definition,...)] [table_options] [select_statement] create_definition: col_name type [NOT NULL | NULL] [DEFAULT default_value] [AUTO_INCREMENT] [PRIMARY KEY] [reference_definition] or PRIMARY KEY (index_col_name,...) or KEY...
hive> CREATE TABLE IF NOT EXISTS employee ( eid int, name String, salary String, destination String) COMMENT ‘Employee details’ ROW FORMAT DELIMITED FIELDS TERMINATED BY ‘\t’ LINES TERMINATED BY ‘\n’ STORED AS TEXTFILE; 1. 2.
DROPTABLEIFEXISTSt;CREATETABLEIFNOTEXISTSt ( avarchar(5) );INSERTINTOtVALUES('holo'), ('gres');ALTERTABLEtALTERCOLUMNa TYPE text; 重命名 ALTER TABLE语句可以对表进行重命名,如果目标表不存在,或者重命名目标表为已存在的表名称,系统均会返回异常。
CREATE TABLE IF NOT EXISTS `runoob_tbl`( `runoob_id` INT UNSIGNED AUTO_INCREMENT, `runoob_title` VARCHAR(100) NOT NULL, `runoob_author` VARCHAR(40) NOT NULL, `submission_date` DATE, PRIMARY KEY ( `runoob_id` ) )ENGINE=InnoDB DEFAULT CHARSET=utf8; ...