When adding columns we must also specify the data type of the column. Ourcolorcolumn will be a string, and we specify string types with theVARCHARkeyword. we also want to restrict the number of characters to 255: Example Add a column namedcolor: ...
添加列的函数ATExecAddColumn,该函数对此进行限制的地方: 也就是宏MaxHeapAttributeNumber定义:#define MaxHeapAttributeNumber 1600 从上图可以看到限制的值来自pg_class系统表的relnatts字段。新增字段时,会对该字段进行更新:仍旧是ATExecAddColumn函数中: Drop表时会对该字段进行更新吗?接着检查函数ATExecDropColumn,...
也就是宏MaxHeapAttributeNumber定义:#define MaxHeapAttributeNumber1600从上图可以看到限制的值来自pg_class系统表的relnatts字段。新增字段时,会对该字段进行更新:仍旧是ATExecAddColumn函数中: Drop表时会对该字段进行更新吗?接着检查函数ATExecDropColumn,该函数将列删除后,并没有更新pg_class系统表的relnatts字段。
Summary: in this tutorial, you will learn how to use the PostgreSQL ADD COLUMN statement to add one or more columns to an existing table. Introduction to the PostgreSQL ADD COLUMN statement To add a new column to an existing table, you use the ALTER TABLE ADD COLUMN statement as follows:...
alter table zyj."a34" add column v_tinyint int; alter table zyj."a34" alter column addr set default 'aaa'; create unique index idxu_tinyint on zyj.a34(v_tinyint); --创建唯一键 alter table zyj."a34" add CONSTRAINT cons_unique unique(v_number); ...
添加新的列:如果要插入的参数是一个新的列,可以使用ALTER TABLE命令的ADD COLUMN子句来添加新的列。例如,以下命令将在表中添加一个名为"new_param"的新列: 添加新的列:如果要插入的参数是一个新的列,可以使用ALTER TABLE命令的ADD COLUMN子句来添加新的列。例如,以下命令将在表中添加一个名为"new_param"的...
v1 number; begin v1:=dbms_random.value(1,100); if v1 >95 then return '1等奖'; elsif v1>85 then return '2等奖'; elsif v1>70 then return '3等奖'; else return '谢谢惠顾'; end if; end;select fun_ran from dual 1.
ALTERTABLEtable_nameALTERCOLUMNcolumn_name TYPE new_data_type USING expression; 我们先为产品表增加一个字符串类型的字段level,然后将其修改为整数类型。 test=#ALTERTABLEproductsADDCOLUMNlevelVARCHAR(10);ALTERTABLEtest=#ALTERTABLEproductsALTERCOLUMNlevelTYPEINTEGER; ...
postgres=# create temp sequence if not exists tmp_seq; postgres=# alter sequence tmp_seq restart with 1; postgres=# alter table test add column col1 int; ALTER TABLE postgres=# update test set col1=nextval('tmp_seq'); UPDATE 10000000 postgres=# select * from test limit 10; id | info...
--语法:alter table table_name add [constraint constraint_name] primary key(column_1, column_2); create table "SysUser"( "UserId" serial, "UserName" varchar(50), "Pwd" varchar(50) ); alter table "SysUser" add constraint PK_SysUser primary key("UserId"); ...