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MySQLi Articles
Page 323 of 341
MySQL - Changing year of dates from 2020 to 2011?
You can change year of dates from 2020 to 2011 using SUBDATE() with INTERVAL of 9 year because there is a difference of 9 years between 2020 to 2011.The syntax is as follows:UPDATE yourTableName SET yourDateColumnName=SUBDATE(yourDateColumnName, INTERVAL 9 YEAR);To understand the above syntax, let us create a table. The query to create a table is as follows:mysql> create table ChangeYearFrom2020To2011 -> ( -> Id int NOT NULL AUTO_INCREMENT, -> ExpiryDate date, -> PRIMARY KEY(Id) -> ); Query OK, 0 rows affected (0.67 sec)Insert some records in the table using insert command. The query to insert ...
Read MoreWhy MySQL NOT NULL shouldn't be added to primary key field?
You do not need to add NOT NULL to primary key field because it gets NOT NULL automatically. Primary key is combination of both NOT NULL and Unique Key.Here is the demo of primary key field. Let us first create a table. The query to create a table is as follows:mysql> create table NotNullAddDemo -> ( -> Id int AUTO_INCREMENT, -> PRIMARY KEY(Id) -> ); Query OK, 0 rows affected (0.81 sec)In the above table, you do not need to add NOT NULL to primary key field because MySQL internally converts it into NOT NULL. To ...
Read MoreFind all the names beginning with the letter 'a' or 'b' or 'c' using MySQL query?
You need to use LIKE with OR operator to find all the names that starts with a or b or c. The syntax is as follows:SELECT *FROM yourTableName WHERE yourColumnName like 'A%' or yourColumnName like 'B%' or yourColumnName like 'C%';The above query finds all names that starts only with the letter ‘a’ or ‘b’ or ‘c’. To understand the above syntax, let us create a table. The query to create a table is as follows:mysql> create table AllNamesStartWithAorBorC -> ( -> Id int NOT NULL AUTO_INCREMENT, -> EmployeeName varchar(20), -> PRIMARY KEY(Id) -> ); Query ...
Read MoreHow to deal with 'Boolean' values in PHP & MySQL?
We are using MySQL version 8.0.12. Let us first check the MySQL version:mysql> select version(); +-----------+ | version() | +-----------+ | 8.0.12 | +-----------+ 1 row in set (0.00 sec)To deal with Boolean in MySQL, you can use BOOL or BOOLEAN or TINYINT(1). If you use BOOL or BOOLEAN, then MySQL internally converts it into TINYINT(1).In BOOL or BOOLEAN data type, if you use true literal then MySQL represents it as 1 and false literal as 0 like in PHP/ C/ C++ language.To proof that MySQL convert the BOOL or BOOLEAN to TINYINT(1), let us create a table with ...
Read MoreConditional 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, ...
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