ALTERTABLEtable_name RENAMECOLUMNold_column_nameTOnew_column_name; 示例: 将middle_name列重命名为second_name: ALTERTABLEemployees RENAMECOLUMNmiddle_nameTOsecond_name; 6. 添加和删除约束 6.1 添加约束 要向表中添加约束,可以使用以下语法: ALTERTABLEtable_nameADDCONSTRAINTconstraint_name constraint_definition...
In Postgres, theALTER TABLEstatement is used to alter/update the table’s structure. Using this command, you can easily modify the structure of any Postgres table, including adding columns, renaming columns/table, dropping columns, modifying constraints, and so on. This blog post will discuss va...
InPostgreSQL, theALTER TABLEcommand performs different functionalities on a table. For example, theALTER TABLEstatement can add, drop, or update the table columns. Moreover, it allows us to add or remove constraints to a table. So, all in all, we can say that theALTER TABLEcommand is used...
ALTERTABLEdistributorsADDCONSTRAINTdistfkFOREIGNKEY(address)REFERENCESaddresses(address) MATCHFULL 兼容性 SQL92ADDCOLUMN形式是兼容的,除了上面说的缺省(值)和约束外。ALTERCOLUMN形式是完全兼容的。 SQL92 对ALTERTABLE声明了一些附加的Postgres目前还不直接支持的功能: ALTERTABLEtableDROPCONSTRAINTconstraint{RESTRICT|CASCAD...
在PostgreSQL中,ALTER TABLE命令用于修改现有表的结构。当对表进行大规模修改时,可能会导致ALTER TABLE执行变慢的情况。 Alter Table太慢可能由以下几个因素引起:...
CREATETABLEPRU(id bigserial,ATEXT);INSERTINTOPRU(A)VALUES('111');INSERTINTOPRU(A)VALUES('111'); Generate rows until 2M, by looping the following statement: INSERTINTOPRUSELECT*FROMPRU; We want to change column A's datatype: ALTER/*optionA*/TABLEPRUALTERCOLUMNA...
ALTERTABLEdistributorsADDCONSTRAINTdistfkFOREIGNKEY(address)REFERENCESaddresses(address) MATCHFULL 兼容性 SQL92ADDCOLUMN形式是兼容的,除了上面说的缺省(值)和约束外。ALTERCOLUMN形式是完全兼容的。 SQL92 对ALTERTABLE声明了一些附加的Postgres目前还不直接支持的功能: ...
Last update on August 19 2022 21:50:35 (UTC/GMT +8 hours) 2. Write a SQL statement to add a column region_id to the table locations.Here is the structure of the table locations.postgres=# \d locations Column | Type | Modifiers ---+---+--- location_id | numeric(4,0) | stree...
2 建议将字段更换为text字段,(或者经常需要变动的文字的字段),ALTER TABLE test ALTER COLUMN puzzle TYPE text;ALTER TABLE test ADD CONSTRAINT checksum_lengthCHECK (LENGTH(puzzle) <= 32);我们先看看这个方法合适吗,这个方法当然合适,字段的扩充可以换个思路,我们可以给的无限,然后后面通过约束限制一下,这样DBA...
ALTER TABLE distributors RENAME COLUMN address TO city; 1. 对现存表改名: ALTER TABLE distributors RENAME TO suppliers; 1. 兼容性 SQL92 ADD COLUMN形式是兼容的,除了上面说的缺省(值)和约束外。ALTER COLUMN形式是完全兼容的。 SQL92 对ALTER TABLE声明了一些附加的Postgres目前还不支持的功能: ...