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MySQL Articles
Page 337 of 355
Conditional select between dates in MySQL for maximum and minimum values of price set in a table?
You need to use CASE statement to conditional select between dates to find the minimum and maximum price. Wrap up the CASE statement with aggregate function MIN() and MAX(). The syntax is as follows:SELECT MIN(CASE WHEN CURDATE() BETWEEN yourStartDateColumnName AND yourEndDateColumnName THEN yourLowPriceColumnName ELSE yourHighPriceColumnName END) AS anyVariableName, MAX(CASE WHEN CURDATE() BETWEEN yourStartDateColumnName AND yourEndDateColumnName THEN yourLowPriceColumnName ELSE yourHighPriceColumnName END) AS anyVariableName FROM yourTableName;To understand the above syntax, let us create a table. The query to create a table is as follows:mysql> create table ConditionalSelect -> ( -> Id int NOT NULL AUTO_INCREMENT, -> StartDate datetime, ...
Read MoreHow to set global event_scheduler=ON even if MySQL is restarted?
There is a single way by which you can set a global event_scheduler=ON even if MySQL is restarted. You need to set global system variable ON and need to use this system variable even if MySQL restart.For this, I am using system variable @@event_scheduler using select statement. The query is as follows:mysql> select @@event_scheduler;The following is the output:+-------------------+ | @@event_scheduler | +-------------------+ | ON | +-------------------+ 1 row in set (0.00 sec)Now, restart MySQL. The query is as follows:mysql> restart; Query OK, 0 rows affected ...
Read MoreHow can I see global locks in MySQL (innodb)?
In order to see the global locks in MySQL (Innodb), use the SHOW command. The below query shows the global locks as well owner of locks and waiters. The following query will also show transaction id and more related to Innodb.The query is as follows:mysql> SHOW ENGINE INNODB STATUS\GThe following is the output:*************************** 1. row *************************** Type: InnoDB Name: Status: ===================================== 2019-01-23 14:46:58 0x2914 INNODB MONITOR OUTPUT ===================================== Per second averages calculated from the last 23 seconds ----------------- BACKGROUND THREAD ----------------- srv_master_thread loops: 87 srv_active, 0 srv_shutdown, 51953 srv_idle srv_master_thread log flush and writes: 0 ---------- SEMAPHORES ---------- OS WAIT ...
Read MoreThe equivalent of SQL Server function SCOPE_IDENTITY() in MySQL?
The equivalent of SQL Server function SCOPE_IDENTITY() is equal to LAST_INSERT_ID() in MySQL. The syntax is as follows:SELECT LAST_INSERT_ID().This returns the id of last inserted record.Here, I am going to create a table with primary key column. The following is the demo of last_insert_id().First, let us create two tables. The query to create the first table table is as follows:mysql> create table TestOnLastInsertIdDemo -> ( -> StudentId int NOT NULL AUTO_INCREMENT, -> PRIMARY KEY(StudentId) -> ); Query OK, 0 rows affected (0.95 sec)Now creating the second table. The query is as follows:mysql> create table TestOnLastInsertIdDemo2 ...
Read MoreThe difference between 'AND' and '&&' in MySQL?
NOTE: There is only one difference between AND and && is that AND is a standard while && is ownership syntax.Except the above statement, there is no difference between AND and &&. Let us look at all the conditions.The result of AND and && will always be either 1 or 0. As we know the AND and && both are logical operators, if there are more than one operand and any one of them has value 0 then result becomes 0 otherwise 1.Here is the demo of AND and &&.Case 1(a): If both operands are 1. Using AND.The query is ...
Read MoreIn MySQL how to select the top 2 rows for each group?
To select the top 2 rows from each group, use the where condition with subquery. Let us create a table. The query to create a table is as follows:mysql> create table selectTop2FromEachGroup -> ( -> Name varchar(20), -> TotalScores int -> ); Query OK, 0 rows affected (0.80 sec)Now insert some records in the table using insert command. The query is as follows:mysql> insert into selectTop2FromEachGroup values('John', 32); Query OK, 1 row affected (0.38 sec) mysql> insert into selectTop2FromEachGroup values('John', 33); Query OK, 1 row affected (0.21 sec) mysql> insert into selectTop2FromEachGroup values('John', 34); Query OK, ...
Read MoreConvert output of MySQL query to UTF8?
You need to use CAST() or CONVERT() function to convert output of MySQL query to UTF8. Here, I am using MySQL version 8.0.12. Let us first check the version:mysql> select version(); +-----------+ | version() | +-----------+ | 8.0.12 | +-----------+ 1 row in set (0.00 sec)In this if you use utf8 then you will get warning of aliases because it has utf8mb4. Therefore, you can avoid the warning by placing utf8mb4.Note: Never use UTF8. For current versions, use UTF8MB4Here is the syntax to convert output of MySQL query to UTF8:SELECT yourColumnName1, convert(yourColumnName2 USING utf8) as anyVariableName FROM ...
Read MoreCan MySQL automatically convert empty strings to NULL?
You need to use NULLIF() function from MySQL. The syntax is as follows:SELECT NULLIF(yourCoumnName, ’ ’) as anyVariableName from yourTableName;In the above syntax, if you compare empty string( ‘ ‘) to empty string( ‘ ‘), the result will always be NULL. However, if you compare with NULL to empty string( ‘ ‘) then also the result will always be NULL.To understand the above syntax, let us create a table. The query to create a table is as follows:mysql> create table ConvertEmptyStringToNULL -> ( -> Id int NOT NULL AUTO_INCREMENT, -> Name varchar(20), -> PRIMARY KEY(Id) ...
Read MoreHow to match one character in MySQL in place of %?
To match only one character in MySQL, you can use underscore(_) in place of %. The syntax is as follows:SELECT *FROM yourTableName WHERE yourColumnName LIKE ‘yourString_’;To understand the above syntax, let us create a table. The query to create a table is as follows:mysql> create table OneCharactermatchDemo -> ( -> Id int NOT NULL AUTO_INCREMENT, -> PassoutYear year, -> PRIMARY KEY(Id) -> ); Query OK, 0 rows affected (0.76 sec)Insert some records in the table using insert command. The query is as follows:mysql> insert into OneCharactermatchDemo(PassoutYear) values('2008'); Query OK, 1 row affected (0.14 sec) mysql> ...
Read MoreChanging Column in MySQL from int to double?
To change the column in MySQL from int to double you need to use ALTER TABLE command.The syntax is as follows:ALTER TABLE yourTableName modify column yourColumnName DOUBLE NOT NULL;If you want NULL value then remove NOT NULL from the above syntax. The syntax is as follows:ALTER TABLE yourTableName modify column yourColumnName DOUBLE;To understand the above syntax, let us create a table. The query to create a table is as follows:mysql> create table IntToDoubleDemo -> ( -> Id int NOT NULL AUTO_INCREMENT, -> Name varchar(10), -> CylinderVolume int, -> PRIMARY KEY(Id) -> ); Query OK, ...
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