Write a SQL query to create a table with three columns: id, name, and age. Add a primary key constraint on the id column. Write a SQL query to create a table with four columns: product_id, product_name, price, and quantity. Ensure that the price column cannot have negative values...
AI代码解释 ---Table structureforgrade---DROPTABLEIFEXISTS`grade`;CREATETABLE`grade`(`id`int(11)NOTNULLAUTO_INCREMENTCOMMENT'id',`sno`varchar(20)CHARACTERSETutf8COLLATEutf8_unicode_ciNULLDEFAULTNULLCOMMENT'学号',`courseName`varchar(20)CHARACTERSETutf8COLLATEutf8_unicode_ciNULLDEFAULTNULLCOMMENT'课程...
约束 SQL 约束(Constraints) SQL 约束用于规定表中的数据规则。 如果存在违反约束的数据行为,行为会被约束终止。 约束可以在创建表时规定(通过 CREATE TABLE 语句),或者在表创建之后规定(通过 ALTER TABLE 语句)。 SQL CREATE TABLE + CONSTRAINT 语法 CREATE TABLE table_name ( column_name1 SQL语句 database_...
SQL CREATE TABLE UNIQUE Constraint With Alter Table We can also add theUNIQUEconstraint to an existing column using theALTER TABLEcommand. For example, For a Single Column -- add unique constraint to an existing columnALTERTABLECollegesADDUNIQUE(college_id); Here, the SQL command adds theUNIQUEc...
SQL UNIQUE Constraint on CREATE TABLE 下面的 SQL 在“Persons” 表创建时在 “Id_P” 列创建 UNIQUE 约束: MySQL: CREATETABLEPersons(Id_PintNOTNULL,LastNamevarchar(255)NOTNULL,FirstNamevarchar(255),Addressvarchar(255),Cityvarchar(255),UNIQUE(Id_P)) ...
SQL> SELECT owner,constraint_name,constraint_type,table_name,status,deferrable,validated 2 FROM user_constraints 3 ORDER BY table_name; OWNER CONSTRAINT_NAME C TABLE_NAME STATUS DEFERRABLE VALIDATED --- --- - --- --- --- --- ROBINSON SYS_C005543 C TB_CONSTRAINT_1 ENABLED NOT DEFERRABLE ...
TABLE_CATALOG nvarchar(128) 數據表限定符。 TABLE_SCHEMA nvarchar(128) 包含數據表的架構名稱。 重要: 尋找物件架構的唯一可靠方式是查詢 sys.objects 目錄檢視。 TABLE_NAME sysname 資料表名稱。 CONSTRAINT_TYPE varchar(11) 條件約束的類型: CHECK UNIQUE PRIMARY KEY FOREIGN KEY IS_DEFER...
SQL JOIN With AS Alias We can use AS aliases with table names to make our query short and clean. For example, -- use alias C for Customers table -- use alias O for Orders table SELECT C.customer_id, C.first_name, O.amount FROM Customers AS C JOIN Orders AS O ON C.customer_id...
可以在创建表时规定约束(通过 CREATE TABLE 语句),或者在表创建之后也可以(通过 ALTER TABLE 语句)。 我们将主要探讨以下几种约束: NOT NULL UNIQUE PRIMARY KEY FOREIGN KEY CHECK DEFAULT SQL NOT NULL 约束 NOT NULL 约束强制列不接受 NULL 值。
SQL>SELECTowner,constraint_name,constraint_type,table_name,status,deferrable,validated 2FROMuser_constraints 3ORDERBYtable_name; OWNERCONSTRAINT_NAMEC TABLE_NAMESTATUSDEFERRABLEVALIDATED --- --- - --- --- --- --- ROBINSONSYS_C005543C TB_CONSTRAINT_1ENABLEDNOTDEFERRABLE VALIDATED ROBINSONSYS_C0055...