show columns

Show DATABASES: lists the DATABASES on the mysql Server. Show tables [FROM db_name]: Lists TABLES in a database. Show table status [FROM db_name]: lists the TABLE information of a database. Show columns from tbl_name [FROM db_name]: lists the column

Next we will talk about adding constraints in the previous article. 3. Add CONSTRAINT (3) add foreign key CONSTRAINT altertable_nameadd [CONSTRAINT [symbol] FOREIGNKEY [index_name] [index_type] (index_col_name,...) references_definition; example:

Null Value Judgment $ T {type1id }=$ $ Pref {DBH}-> selectrow_array ("select type1id from enq1 where id = 3 "); If ($ t {type1id} = 0 ){ Print "type1id is null \ n "; } ==> This statement is incorrect if it is not a numerical value. Special

1. constraints ensure data integrity and consistency. constraints are classified into table-level constraints and column-level constraints. Constraints include: NOTNULL (non-empty constraint), PRIMARYKEY (primary key constraint), UNIQUEKEY (unique

The judgment of NULL value $t {Type1id} = $ $pref {dbh}->selectrow_array ("Select Type1id from enq1 WHERE id = 3 "); if ($t {type1id} = = 0) { Print "Type1id is null\n"; } ==> is not a numeric term, this statement has a problem. Numeric items are

Let's go on to the previous article on adding a constraint. Three add constraints (3) Adding foreign KEY constraints ALTER TABLE table_name ADD [CONSTRAINT [symbol]] FOREIGN KEY [index_name] [Index_type](Index_col_name,...)

Modifying a data table includes adding a column, deleting a column, adding a constraint, deleting a constraint, modifying a column definition, and modifying a data table name. you must be cautious when using the following two data tables. The

Modifying a data table includes adding columns, deleting columns, adding constraints, deleting constraints, modifying column definitions, and modifying data table names, and the following two when we useBe cautious and try not to use it.Here is a

Original: 5-relevance model1, SectionModel.class.phpTo inherit Relationmodel, the mapping model and class name write correspond to the data table and the action class1PHP2 classSectionmodelextendsrelationmodel{3 Public $_link=Array(4'

Detailed description of the use of the ALTER command in MySQL, mysqlalter MySQL's ALTER command is very useful when you want to change the table name, table fields, or if you want to add or delete columns in an existing table. Let's start to create

MySQL is a relational database (RelationalDatabaseManagementSystem ). This article focuses on the alert commands of the mysql Database. This article is very detailed and has reference value. if you are interested, join us and learn that MySQL is a

MySQL database ALTER command explanation, MySQL ALTER command explanation MySQL is a Relational Database Management System. This so-called "Relational" can be understood as "tables". A Relational Database consists of one or more tables. When we need

MySQL's alter command is very useful when you want to change the name of the table, the field of the table, or if you want to add or delete columns from an existing table. Let's start by creating a use case with a table named Testalter_tbl:

Work with data tablesBasic Database OperationsWith MySQL, currently (version 3.23) You can choose between three basic database table types. When you create a table, you can tell MySQL which table type it should use for the table. MySQL will always

When creating a table, MySQL creates a. frm file to save the table and column definitions. Indexes are stored in a file with the. MYI (MYindex) Extension and data is stored in a file with the. MYD (MYData) extension. 1. Use the SHOW/DESCRIBE

Show databasesshow tablesinformation_schema The output of the show tables statement does not contain the temporary table.   View all databases on the server > Show databases: view the create database statement of a given database> show create

MySQL ALTER and mysqlalter When we need to modify the data table name or field, we need to use the MySQL ALTER command. Before starting this chapter, let's create a table named testalter_tbl. root@host# mysql -u root -p password;Enter password:******

Mysql database learning-1, obtain the original data bitsCN.com show databasesshow tablesinformation_schemashow tables statement. The output does not contain the temporary table. View all databases on the server.> show databases view the create

Mysql database learning-1, get the original data bitsCN.com Mysql database learning-1. get the original data Show databasesshow tablesinformation_schemashow tables statement output does not contain the temporary table view all the databases on

This article mainly introduces how to use the ALTER command in MySQL, which is the basic knowledge in MySQL beginners. it is very useful for anyone who needs it to refer to the ALTER command in MySQL, if you want to change the table name, table