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Database Articles
Page 496 of 546
What is the syntax for input parameters (variables) in a MySQL query?
To set a variable in MySQL, you need to use the SET command. Following is the syntax:set @yourVariableName:=yourValue; select *from yourTableName where yourColumnName=@yourVariableName;Let us first create a table:mysql> create table DemoTable ( Id int, FirstName varchar(20), LastName varchar(20) ); Query OK, 0 rows affected (0.83 sec)Following is the query to insert some records in the table using insert command:mysql> insert into DemoTable values(10, 'Carol', 'Taylor'); Query OK, 1 row affected (0.18 sec) mysql> insert into DemoTable values(20, 'John', 'Doe'); Query OK, 1 row affected (0.19 sec) mysql> insert into DemoTable values(30, 'John', 'Smith'); Query OK, 1 row ...
Read MoreHow to update a column of varchar type in MySQL to increase its length?
Let us first create a table. Here, we have two columns with varchar type −mysql> create table DemoTable ( UserId int NOT NULL AUTO_INCREMENT PRIMARY KEY, UserFirstName varchar(10), UserLastName varchar(20) , UserAge int ); Query OK, 0 rows affected (0.96 sec)Let us check the description of table using DESC command −mysql> desc DemoTable;This will produce the following output −+---------------+-------------+------+-----+---------+----------------+ | Field | Type | Null | Key | Default | Extra | +---------------+-------------+------+-----+---------+----------------+ | UserId | int(11) | NO ...
Read MoreHow to GROUP BY in a select query on positive or negative values?
Following is the syntax to GROUP BY in a select query on positive or negative values:select *from yourTableName group by -yourColumnName;Let us first create a table:mysql> create table DemoTable (Value int); Query OK, 0 rows affected (0.60 sec)Following is the query to insert some records in the table using insert command:mysql> insert into DemoTable values(-10); Query OK, 1 row affected (0.20 sec) mysql> insert into DemoTable values(-20); Query OK, 1 row affected (0.10 sec) mysql> insert into DemoTable values(20); Query OK, 1 row affected (0.13 sec) mysql> insert into DemoTable values(10); Query OK, 1 row affected (0.13 sec) mysql> insert ...
Read MoreHow to order by certain part of a string in MySQL?
You can use ORDER BY SUBSTRING() to order by certain part of a string in MySQL. Let us first create a table:mysql> create table DemoTable (UserId varchar(200)); Query OK, 0 rows affected (0.68 sec)Following is the query to insert records in the table using insert command:mysql> insert into DemoTable values('USER_1234'); Query OK, 1 row affected (0.13 sec) mysql> insert into DemoTable values('USER_John'); Query OK, 1 row affected (0.19 sec) mysql> insert into DemoTable values('USER_Sam'); Query OK, 1 row affected (0.22 sec) mysql> insert into DemoTable values('USER_Carol'); Query OK, 1 row affected (0.16 sec) mysql> insert into DemoTable values('USER_Bob'); Query OK, ...
Read MoreWhich datatype should I use for flag in MySQL?
To set a flag, you can set the type as tinyint(1) type. Following is the syntax −yourColumnName tinyint(1) DEFAULT 1;Let us first create a table −mysql> create table DemoTable ( ClientId int NOT NULL AUTO_INCREMENT PRIMARY KEY, ClientName varchar(20), isMarried tinyint(1) DEFAULT 1 ); Query OK, 0 rows affected (0.64 sec)Insert some records in the table using insert command −mysql> INSERT INTO DemoTable(ClientName, isMarried) values('Larry', 0); Query OK, 1 row affected (0.16 sec) mysql> INSERT INTO DemoTable(ClientName) values('David'); Query OK, 1 row affected (0.12 sec) mysql> INSERT INTO DemoTable(ClientName, isMarried) values('Mike', 1); Query OK, 1 row affected (0.19 ...
Read MoreHow can I remove every column in a table in MySQL?
In order to remove every column in a table in MySQL, you can use DROP TABLE command. Following is the syntax:DROP TABLE yourTableName;Let us first create a table:mysql> create table DemoTable ( StudentId int NOT NULL AUTO_INCREMENT PRIMARY KEY, StudentFirstName varchar(20), StudentLastName varchar(20), StudentAge int, StudentAddress varchar(200), StudentCountryName varchar(30), StudentDateOfBirth datetime ); Query OK, 0 rows affected (0.85 sec)Let us check the description of table using DESC command:mysql> desc DemoTable;This will produce the following output:+--------------------+--------------+------+-----+---------+----------------+ | Field | Type | Null | Key ...
Read MoreUpdate one column data to another column in MySQL if the second column is NOT NULL?
To update one column data to another column, you can use UPDATE command. Let us first create a table −mysql> create table DemoTable ( UserId int NOT NULL AUTO_INCREMENT PRIMARY KEY, UserFirstName varchar(20), ListOfName varchar(20) ); Query OK, 0 rows affected (0.59 sec)Insert some records in the table using insert command −mysql> insert into DemoTable(UserFirstName, ListOfName) values('John', 'Larry'); Query OK, 1 row affected (0.29 sec) mysql> insert into DemoTable(UserFirstName, ListOfName) values('Carol', null); Query OK, 1 row affected (0.14 sec) mysql> insert into DemoTable(UserFirstName, ListOfName) values('David', 'Sam'); Query OK, 1 row affected (0.22 sec) mysql> insert into DemoTable(UserFirstName, ListOfName) ...
Read MoreCan I write my own MySQL functions to use in MySQL queries?
Yes, you can write own MySQL function to use in MySQL queries. Following is the syntax:DELIMITER // CREATE FUNCTION yourFunctionName(optional parameters)) RETURNS yourDataType DETERMINISTIC NO SQL BEGIN yourStatements1 . . . . N END // DELIMITER ;We have used the CREATE FUNCTION above to create a custom function.Let us create a custom MySQL function to use in MySQL query:mysql> DELIMITER // mysql> CREATE FUNCTION get_First_Name(Name VARCHAR(255)) RETURNS VARCHAR(255) DETERMINISTIC NO SQL BEGIN RETURN LEFT(Name, LOCATE(' ', Name) - 1); END // Query OK, 0 rows affected (0.20 sec) mysql> DELIMITER ;Now call ...
Read MoreHow to create MySQL user with limited privileges?
To create MySQL user with limited privileges, following is the syntax −CREATE USER 'yourUserName'@'yourHostName' IDENTIFIED BY 'yourPassword';Following is the syntax to set limited privileges for user −GRANT SELECT, INSERT, UPDATE, etc. REFERENCES ON yourDatabaseName.* TO 'yourUserName'@'yourHostName';Let us implement the above syntaxes in order to create a MySQL user with limited privileges −mysql> CREATE USER 'David'@'localhost' IDENTIFIED BY 'david'; Query OK, 0 rows affected (0.20 sec) mysql> GRANT SELECT, INSERT, UPDATE, DELETE, ALTER, CREATE, REFERENCES ON test.* TO 'David'@'localhost'; Query OK, 0 rows affected (0.21 sec)Let us check the user has been created with name ‘David’ or not.mysql> ...
Read MoreHow to SELECT records if the absolute value of the difference between two values is greater than a certain number?
To SELECT records if the absolute value of the difference between two values is greater than a certain number, following is the syntax:select *from yourTableName where abs(yourColumnName1-yourColumnName2) >= yourCertainNumber;Let us first create a table:mysql> create table DemoTable ( Number1 int , Number2 int ); Query OK, 0 rows affected (0.59 sec)Following is the query to insert some records in the table using insert command:mysql> insert into DemoTable values(10, 20); Query OK, 1 row affected (0.18 sec) mysql> insert into DemoTable values(100, 200); Query OK, 1 row affected (0.13 sec) mysql> insert into DemoTable values(400, 300); Query OK, 1 ...
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