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MySQL query data

The MySQL database uses SQL SELECT statements to query data.

You can query the data in the database from the mysql > command prompt window, or query the data through the PHP script.

Grammar

The following is the common SELECT syntax for querying data in an MySQL database:

SELECT column_name,column_nameFROM table_ name[WHERE Clause] [LIMIT N] [OFFSET M]

You can use one or more tables in the query statement, split the tables with commas (,), and use the where statement to set the query conditions.

The SELECT command can read one or more records.

You can use an asterisk (*) instead of other fields, and the SELECT statement returns all the field data of the table

You can use the WHERE statement to include any condition.

You can use the LIMIT property to set the number of records returned.

You can specify the data offset to start the query with the SELECT statement through OFFSET. The offset is 0 by default.

Get data from the command prompt

For the following example, we will obtain the data of the MySQL data table runoob_tbl through the SQL SELECT command:

Example

The following example returns all records of the data table runoob_tbl:

Read the data table:

Select * from runoob_tbl

Output result:

Use PHP script to get data

Use the mysqli_query () and SQL SELECT commands of the PHP function to get the data.

This function is used to execute the SQL command, and then use or output the data of all queries through the PHP function mysqli_fetch_array ().

The mysqli_fetch_array () function takes a row from the result set as an associative array, or an array of numbers, or both, returns an array generated from rows fetched from the result set, or false if there are no more rows.

The following example reads all records from the data table runoob_tbl.

Example

Try the following example to display all records of the data table runoob_tbl.

Use the mysqli_fetch_array MYSQL_ASSOC parameter to get the data:

}

Echo''

Mysqli_close ($conn)

? >

The output is as follows:

In the above example, each row of records read is assigned to the variable $row, and then each value is printed out.

Note: remember that if you need to use a variable in a string, put the variable in curly braces.

In the above example, the second parameter of the PHP mysqli_fetch_array () function is MYSQL_ASSOC, which is set to return an associative array. You can use the field name as the index of the array.

PHP provides another function, mysqli_fetch_assoc (), which takes a row from the result set as an associative array. Returns an associative array generated from rows fetched from the result set, or false if there are no more rows.

Example

Try the following example, which uses the mysqli_fetch_assoc () function to output all records of the data table runoob_tbl:

Use mysqli_fetch_assoc to get data:

The output is as follows:

You can also use the constant MYSQL_NUM as the second argument to the PHP mysqli_fetch_array () function, which returns an array of numbers.

Example

The following example uses the MYSQL_NUM parameter to display all records of the data table runoob_tbl:

Use the mysqli_fetch_array MYSQL_NUM parameter to get the data:

The output is as follows:

The output of the above three instances is the same.

Memory release

It is a good habit to free cursor memory after we have executed the SELECT statement.

Memory can be freed through the PHP function mysqli_free_result ().

The following example demonstrates the use of this function.

Example

Try the following example:

Use mysqli_free_result to free memory:

The output is as follows:

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