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Database Articles
Page 335 of 547
How to derive value of a field from another field in MySQL?
For this, you can use the concept of user defined variable. Let us first create a table −mysql> create table DemoTable1868 ( Value int ); Query OK, 0 rows affected (0.00 sec)Insert some records in the table using insert command −mysql> insert into DemoTable1868 values(10); Query OK, 1 row affected (0.00 sec) mysql> insert into DemoTable1868 values(20); Query OK, 1 row affected (0.00 sec) mysql> insert into DemoTable1868 values(30); Query OK, 1 row affected (0.00 sec) mysql> insert into DemoTable1868 values(40); Query OK, 1 row affected (0.00 sec)Display all records from the table using ...
Read MoreHow to list all variables initialized by SET operator in MySQL?
To list all variables initialized by SET operator, the syntax is as follows −select * from performance_schema.user_variables_by_thread;Here is the query to set the variable −mysql> set @FirstName='John'; Query OK, 0 rows affected (0.00 sec) mysql> set @LastName='Doe'; Query OK, 0 rows affected (0.00 sec)Here is the query to display the list of all variables initialized by SET operator. This list includes the variables set above −mysql> select * from performance_schema.user_variables_by_thread;This will produce the following output −+-----------+---------------+----------------+ | THREAD_ID | VARIABLE_NAME | VARIABLE_VALUE | +-----------+---------------+----------------+ | 120 | TotalAmount | 5000 | ...
Read MoreIncrement date/time value by second with MySQL query?
For this, use date_add() with interval command. Let us first create a table −mysql> create table DemoTable1867 ( ArrivalTime datetime ); Query OK, 0 rows affected (0.00 sec)Insert some records in the table using insert command −mysql> insert into DemoTable1867 values('2019-10-12 12:34:45'); Query OK, 1 row affected (0.00 sec) mysql> insert into DemoTable1867 values('2019-10-12 10:04:15'); Query OK, 1 row affected (0.00 sec) mysql> insert into DemoTable1867 values('2019-10-12 11:00:23'); Query OK, 1 row affected (0.00 sec)Display all records from the table using select statement −mysql> select * from DemoTable1867; This will produce the following output ...
Read MoreMySQL query to get string from one column and find its position in another column with comma separated values?
For this, use FIND_IN_SET(). Let us first create a table −mysql> create table DemoTable1866 ( Value1 int, ListOfValues varchar(100) ); Query OK, 0 rows affected (0.00 sec)Insert some records in the table using insert command −mysql> insert into DemoTable1866 values(56, '78, 56, 98, 95'); Query OK, 1 row affected (0.00 sec) mysql> insert into DemoTable1866 values(103, '103, 90, 102, 104'); Query OK, 1 row affected (0.00 sec) mysql> insert into DemoTable1866 values(77, '34, 45, 77, 78'); Query OK, 1 row affected (0.00 sec)Display all records from the table using select statement −mysql> ...
Read MoreHow to assign the result of a MySQL query into a variable?
Use @anyVariableName to assign the result of a query into a variable. Let us first create a table −mysql> create table DemoTable1864 ( Id int, FirstName varchar(20), LastName varchar(20) ); Query OK, 0 rows affected (0.00 sec)Insert some records in the table using insert command −mysql> insert into DemoTable1864 values(101, 'Chris', 'Brown'); Query OK, 1 row affected (0.00 sec) mysql> insert into DemoTable1864 values(102, 'David', 'Miller'); Query OK, 1 row affected (0.00 sec) mysql> insert into DemoTable1864 values(103, 'Adam', 'Smith'); Query OK, 1 row affected (0.00 sec) mysql> insert into ...
Read MoreHow to set default value for empty row in MySQL?
To set default value for empty row, use the concept of COALESCE(). Let us first create a table −mysql> create table DemoTable1863 ( FirstName varchar(20) ); Query OK, 0 rows affected (0.00 sec)Insert some records in the table using insert command −mysql> insert into DemoTable1863 values('Chris'); Query OK, 1 row affected (0.00 sec) mysql> insert into DemoTable1863 values(NULL); Query OK, 1 row affected (0.00 sec) mysql> insert into DemoTable1863 values('David'); Query OK, 1 row affected (0.00 sec) mysql> insert into DemoTable1863 values(NULL); Query OK, 1 row affected (0.00 sec)Display all records from the table ...
Read MoreHow to find records with a null value in a set of columns with MySQL
For this, use the concept of GREATEST(). Let us first create a table −mysql> create table DemoTable1862 ( Value1 int, Value2 int, Value3 int, Value4 int ); Query OK, 0 rows affected (0.00 sec)Insert some records in the table using insert command −mysql> insert into DemoTable1862 values(43, 34, 56, 42); Query OK, 1 row affected (0.00 sec) mysql> insert into DemoTable1862 values(NULL, 78, 65, NULL); Query OK, 1 row affected (0.00 sec) mysql> insert into DemoTable1862 values(110, NULL, 78, NULL); Query OK, 1 row affected (0.00 sec)Display all ...
Read MoreHow to find rows with exact value in one or more columns with MySQL?
For this, you can use GROUP BY HAVING with subquery. Let us first create a table −mysql> create table DemoTable1861 ( Id int NOT NULL AUTO_INCREMENT PRIMARY KEY, Name varchar(20), Marks int ); Query OK, 0 rows affected (0.00 sec)Insert some records in the table using insert command −mysql> insert into DemoTable1861(Name, Marks) values('John', 45); Query OK, 1 row affected (0.00 sec) mysql> insert into DemoTable1861(Name, Marks) values('Chris', 74); Query OK, 1 row affected (0.00 sec) mysql> insert into DemoTable1861(Name, Marks) values('David', 89); Query OK, 1 row affected (0.00 sec) ...
Read MoreHow to use an OUT parameter / read data with SELECT from table in a MySQL procedure?
For this, you can use SELECT INTO. Let us first create a table −mysql> create table DemoTable1860 ( Amount int ); Query OK, 0 rows affected (0.00 sec)Insert some records in the table using insert command −mysql> insert into DemoTable1860 values(1590); Query OK, 1 row affected (0.00 sec) mysql> insert into DemoTable1860 values(410); Query OK, 1 row affected (0.00 sec) mysql> insert into DemoTable1860 values(3000); Query OK, 1 row affected (0.00 sec)Display all records from the table using select statement −Mysql> select * from DemoTable1860; This will produce the following output −+--------+ | Amount ...
Read MoreIs there an easy way to rename a table in a MySQL procedure?
Yes, use the ALTER command with RENAME. Let us first create a table −mysql> create table DemoTable1859 ( Id int ); Query OK, 0 rows affected (0.00 sec)Insert some records in the table using insert command −mysql> insert into DemoTable1859 values(101); Query OK, 1 row affected (0.00 sec) mysql> insert into DemoTable1859 values(102); Query OK, 1 row affected (0.00 sec)Display all records from the table using select statement −mysql> select * from DemoTable1859; This will produce the following output −+------+ | Id | +------+ | 101 | | 102 | +------+ 2 rows ...
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