do_command(sql_parse.cc) ->dispatch_command(sql_parse.cc) ->mysql_parse(sql_parse.cc) ->mysql_execute_command(sql_parse.cc) ->mysql_create_table(sql_table.cc) ->mysql_create_table_nolock(sql_table.cc),这里会持有LOCK_open ->rea_create_table(unireg.cc) ->mysql_create_frm(unireg.c...
Here, the SQL command checks if a table namedCompaniesexists, and if not, it creates a table with specified columns. Create Table Using Another Existing Table In SQL, we can create a new table by duplicating an existing table's structure. Let's look at an example. -- create a backup t...
If you use the AUTOINC clause to turn on autoincrementing for a field and specify a default value, Visual FoxPro stores the default value in the table but does not use it. Visual FoxPro uses the default value if you use the SQLALTER TABLEcommand to remove autoincrementing for the field....
Oracle PL/SQL:CREATE TABLE statement: create a table with primary key.CREATE TABLE statement can be used to create table objects in database. It is possible to add constraints like primary key ,foreign key while table creation.Primary key is the unique identifier for a row of data.One ...
Visual FoxPro uses the default value if you use the ALTER TABLE - SQL command to remove autoincrementing for the field. PRIMARY KEY | UNIQUE PRIMARY KEY creates a primary index for the field specified in FieldName1. UNIQUE creates a candidate index for the field specified in FieldName1. ...
如果学生表STUDENT是使用下面的SQL语句创建的: Create table student(SNO C(4)) PRIMARY KEY Not Null; S
题目使用下列SQL语句创建教师表: CREATE TABLE 教师表(教师编号 I PRIMARY KEY,; 姓名 C(8) NOT NULL,; 职称 C(10) DEFAULT "讲师") 如果要删除“职称”字段的DEFAULT约束,正确的SQL语句是___。相关知识点: 试题来源: 解析 A 反馈 收藏
PRIMARY KEY 建立欄位的主要索引。 主要索引標籤的名稱與欄位相同。 UNIQUE 建立欄位的候選索引。 候選索引標籤的名稱與欄位相同。 備註 候選索引(在 CREATE TABLE 或 ALTER TABLE - SQL 中包含 UNIQUE 選項所建立的索引,與 INDEX 命令中的 UNIQUE 選項所建立的索引不同。 在 INDEX 命令中使用 UNIQUE 選項建立...
The primary key is always active. SQL Server keeps the table sorted in primary key order and rejects records with duplicate values in primary key fields. That's why the values in the primary key must always be unique. It's not the value in each field in the primary key that must be ...
用下面的T-SQL语句建立一个基本表:CREATE TABLE Student(Sno CHAR(4) PRIMARY KEY,Sname CHAR(8) NOT NUL