unique_add_to_existing.sql ALTER TABLE users ADD CONSTRAINT unique_username UNIQUE (username); The username column must now contain unique values. Dropping Unique ConstraintThis example drops a UNIQUE constraint from a table. unique_drop.sql ...
ALTER TABLE students ALTER COLUMN age DROP DEFAULT; 5、修改字段约束 有时,我们可能需要修改字段的约束条件,如唯一性、非空等,以下是一些常用的修改字段约束的命令: (1)添加唯一约束: ALTER TABLE 表名 ADD CONSTRAINT 约束名 UNIQUE (字段名); 示例: ALTER TABLE students ADD CONSTRAINT unique_email UNIQUE ...
When you add a UNIQUE constraint to a column or a group of columns, PostgreSQL will automatically create a unique index on the column or the group of columns. PostgreSQL UNIQUE constraint example The following statement creates a new table named person with a UNIQUE constraint for the email col...
When you add a UNIQUE constraint to a column or a group of columns, PostgreSQL will automatically create a unique index on the column or the group of columns. PostgreSQL UNIQUE constraint example The following statement creates a new table named person with a UNIQUE constraint for the email col...
ALTER TABLE t_test DROP COLUMN t1; 如果t1字段被另外的表外键引用,直接执行删除会报错,需要使用cascade删除外键的依赖 ALTER TABLE t_test DROP COLUMN t1 cascade; 增加约束 ALTER TABLE t_test ADDCHECK(t2 >0);表示t2得大于0ALTER TABLE t_test ADD CONSTRAINT unique_test_keyUNIQUE(t1);表示t1是唯一约...
ALTER TABLE table_name MODIFY column_name datatype NOT NULL; 给表中某列 ADD UNIQUE CONSTRAINT( 添加 UNIQUE 约束),语法如下: ALTER TABLE table_name ADD CONSTRAINTMyUniqueConstraintUNIQUE(column1,column2...); 给表中 ADD CHECK CONSTRAINT(添加 CHECK 约束),语法如下: ...
The unique constraint in PostgreSQL ensures that the uniqueness of the values entered into a column or a field of a table.
How Does UNIQUE Constraint Work on Multiple Columns in PostgreSQL? Postgres enables us to implement the UNIQUE constraint on more than one column using the following syntax: CREATE TABLE tab_name ( col_1 data_type, col_2 data_type,
endTime := to_char( startTime::timestamp + interval'1 month','YYYY-MM-DD HH24:MI:SS.MS'); strSQL :='CREATE TABLE IF NOT EXISTS'||TG_RELNAME||'_'||curMM||'( CHECK('||time_column_name||'>='''|| startTime ||'''AND'||time_column_name||'<'''|| endTime ||''')) ...
alter table 表名 rename column 字段名 to 新字段名; ALTER TABLE public.table_name RENAME col1 to col10 ; 十二、pg添加主键 代码语言:javascript 代码运行次数:0 运行 AI代码解释 ALTER TABLE public.table_name ADD PRIMARY KEY ("id"); 十三、pg表中的列添加NOT NULL约束 代码语言:javascript 代码运行...