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What Is a Subquery
What Is a Subquery? - MySQL FAQs - SQL SELECT Statements with JOIN and Subqueries A subquery is a SELECT statement used as part of the selection criteria of the main SELECT statement. The subquery specified in the WHERE clause will be evaluated repeated on each row of the selection base table. The o...
2007-05-11, 5639👍, 0💬

How To Turn on Binary Logs
How To Turn on Binary Logs? - MySQL FAQs - Server Daemon mysqld Administration If you want MySQL to write binary logs to a file, you can use the "--log-bin=fileBaseName" option at the "mysqld" command line. The tutorial exercise below shows you a good example on how to use this option: >cd \mysql\bi...
2007-05-11, 5631👍, 0💬

What Is a Result Set Object
What Is a Result Set Object? - MySQL FAQs - Managing Tables and Running Queries with PHP Scripts A result set object is a logical representation of data rows returned by mysql_query() function on SELECT statements. Every result set object has an internal pointer used to identify the current row in t...
2007-05-10, 5629👍, 0💬

What Happens If the UPDATE Subquery Returns No Rows
What Happens If the UPDATE Subquery Returns No Rows? - MySQL FAQs - Understanding SQL INSERT, UPDATE and DELETE Statements If you use a subquery to assign new values in the SET clause in an UPDATE statement, and the subquery returns no rows for an outer row, MySQL will provide a NULL value to the SE...
2007-05-11, 5628👍, 0💬

How To Add a New Column to an Existing Table
How To Add a New Column to an Existing Table? - MySQL FAQs - Understanding SQL CREATE, ALTER and DROP Statements If you have an existing table with existing data rows, and want to add a new column to that table, you can use the "ALTER TABLE ... ADD COLUMN" statement. The tutorial script below shows ...
2007-05-11, 5623👍, 0💬

What Are the Impacts on Applications from Locks, Timeouts, and DeadLocks
What Are the Impacts on Applications from Locks, Timeouts, and DeadLocks? - MySQL FAQs - Transaction Management: Commit or Rollback If you are using transactions with REPEATABLE READ isolation level and transaction safe storage engines in your applications, data locks, lock timeouts, and dead lock d...
2007-05-08, 5618👍, 0💬

How To Write Date and Time Literals
How To Write Date and Time Literals? - MySQL FAQs - Introduction to SQL Date and Time Handling MySQL offers a number of formats for you to use to enter date and time literals: ANSI standard format: "YYYY-MM-DD HH:MM:SS". Non-standard limiters. Like: "YYYY/MM/DD HH^MM^SS" or "YYYY.MM.DD HH-MM-SS". No...
2007-05-11, 5617👍, 0💬

How To Experiment Dead Locks
How To Experiment Dead Locks? - MySQL FAQs - Transaction Management: Commit or Rollback If you want to have some experience with dead locks, you can create two windows running two mysql transactions in two sessions at the REPEATABLE READ transaction isolation level. Then run some UPDATE statements a...
2007-05-09, 5616👍, 0💬

How To View User Privileges
How To View User Privileges? - MySQL FAQs - Managing User Accounts and Access Privileges If a regular user wants to see his/her own granted privileges, he/she can use the "SHOW GRANTS" command. If the "root" user wants to see other user's granted privileges, he/she can use the "SHOW GRANTS FOR userN...
2007-05-10, 5614👍, 0💬

How To Use SELECT Statement to Count the Number of Rows
How To Use SELECT Statement to Count the Number of Rows? - MySQL FAQs - SQL SELECT Query Statements with GROUP BY If you want to count the number of rows, you can use the COUNT(*) function in the SELECT clause. The following tutorial exercise shows you some good example: mysql> SELECT COUNT(*) FROM ...
2007-05-11, 5608👍, 0💬

What Happens If Unique Value Constraints Are Violated
What Happens If Unique Value Constraints Are Violated? - MySQL FAQs - Understanding SQL INSERT, UPDATE and DELETE Statements If you are inserting a new record that has values violating a unique constraint, you will get an error. Note that primary key column has a unique value constraint by default. ...
2007-05-11, 5591👍, 0💬

What Are Date and Time Intervals
What Are Date and Time Intervals? - MySQL FAQs - Introduction to SQL Date and Time Handling A date and time interval is special value to be used to increment or decrement a date or a time at a given date or time unit. A data and time interval should be expression in the format of "INTERVAL expressio...
2007-05-11, 5585👍, 0💬

How To Dump a Table to a File with "mysqldump"
How To Dump a Table to a File with "mysqldump"? - MySQL FAQs - Administrator Tools for Managing MySQL Server If you want to dump all rows in a table from the server to a file, you can use "mysqldump" with the "-f fileName" option as show in the following tutorial exercise: >cd \mysql\bin >mysqldump ...
2007-05-11, 5578👍, 0💬

How To Include Comments in SQL Statements
How To Include Comments in SQL Statements? - MySQL FAQs - Introduction to SQL Basics If you want to include comments in a SQL statement, you can first enter "--", then enter your comment until the end of the line. The tutorial exercise below shows you some good examples: SELECT 'Hello world!' FROM D...
2007-05-11, 5569👍, 0💬

How Many Ways to Get the Current Time
How Many Ways to Get the Current Time? - MySQL FAQs - Introduction to SQL Date and Time Handling There are 8 ways to get the current time: SELECT NOW() FROM DUAL; 2006-07-01 10:02:41 SELECT CURRENT_TIME() FROM DUAL; 10:02:58 SELECT SYSDATE() FROM DUAL; 2006-07-01 10:03:21 mysql> SELECT CURRENT_TIMES...
2007-05-11, 5567👍, 0💬

How To Start MySQL Server Daemon mysqld
How To Start MySQL Server Daemon mysqld? - MySQL FAQs - Server Daemon mysqld Administration There are a number of ways to start MySQL server daemon, mysqld: Double click on the file name, mysqld.exe, in a file explorer window. This is an easy way to start the server. But you will not be able to spec...
2007-05-11, 5555👍, 0💬

What Is "mysqladmin"
What Is "mysqladmin"? - MySQL FAQs - Administrator Tools for Managing MySQL Server "mysqladmin" is a command-line interface for administrators to perform server administration tasks. It support a number of commonly used commands like: "mysqladmin shutdown" - Shuts down the server. "mysqladmin ping" ...
2007-05-11, 5548👍, 0💬

What Happens If the UPDATE Subquery Returns Multiple Rows
What Happens If the UPDATE Subquery Returns Multiple Rows? - MySQL FAQs - Understanding SQL INSERT, UPDATE and DELETE Statements If a subquery is used in a UPDATE statement, it must return exactly one row for each row in the update table that matches the WHERE clause. If it returns multiple rows, My...
2007-05-11, 5535👍, 0💬

What Are Numeric Data Types
What Are Numeric Data Types? - MySQL FAQs - Introduction to SQL Basics MySQL supports the following numeric data types: BIT(n) - An integer with n bits. BOOL same as BOOLEAN - Boolean values stored in 1 bit. TINYINT - A small integer stored in 1 byte. SMALLINT - A small integer stored in 2 bytes. ME...
2007-05-11, 5534👍, 0💬

What Are NULL Values
What Are NULL Values? - MySQL FAQs - Introduction to SQL Basics NULL is a special value that represents no value. Here are basic rules about NULL values: NULL presents no value. NULL is not the same as an empty string ''. NULL is not the same as a zero value 0. NULL can be used as any data type. NUL...
2007-05-11, 5533👍, 0💬

What Are Date and Time Functions
What Are Date and Time Functions? - MySQL FAQs - Introduction to SQL Date and Time Handling MySQL offers a number of functions for date and time values: ADDDATE(date, INTERVAL expr unit) - Adding days to a date. Same as DATE_ADD(). ADDTIME(time1, time2) - Adding two time values together. CURDATE() -...
2007-05-11, 5531👍, 0💬

How To Turn on Query Logs
How To Turn on Query Logs? - MySQL FAQs - Server Daemon mysqld Administration If you want MySQL to write query logs to a file, you can use the "--log=fileName" option at the "mysqld" command line. The tutorial exercise below shows you a good example on how to use this option and view the query log f...
2007-05-11, 5523👍, 0💬

How To Turn on Error Logs
How To Turn on Error Logs? - MySQL FAQs - Server Daemon mysqld Administration If you want MySQL to write critical errors into a log file, you can use the "--log-error=fileName" option at the "mysqld" command line. The tutorial exercise below shows you a good example on how to use this option: >cd \m...
2007-05-11, 5521👍, 0💬

What Is a Data Lock
What Is a Data Lock? - MySQL FAQs - Transaction Management: Commit or Rollback MySQL uses two types of data locks at two levels to provide you the transaction isolation level you need: Share Lock at Row Level (S) - A data row is locked by a transaction for reading. Exclusive Lock at Row Level (X) - ...
2007-05-09, 5521👍, 0💬

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