To make a pair of columns unique, use UNIQUE with ALTER TABLE command. Following is the syntax −alter table yourTableName add unique yourUniqueName(yourColumnName1, yourColumnName2, ...N);Let us first create a table −mysql> create table DemoTable (    StudentId int NOT NULL AUTO_INCREMENT PRIMARY KEY,    StudentFirstName varchar(100),    StudentLastName varchar(100),    StudentAge int,    StudentPhoneNumber varchar(20) ); Query OK, 0 rows affected (0.81 sec)Following is the query to make a pair of unique columns in MySQL −mysql> alter table DemoTable add unique DemoTable_unique_StudentFirstName_StudentPhoneNumber(StudentFirstName, StudentPhoneNumber); Query OK, 0 rows affected (0.40 sec) Records: 0 Duplicates: 0 Warnings: 0Insert some records in the ... Read More

Let us first see when this situation can arise. Create a table and set column name with datatype but without the size −mysql> create table DemoTable (    Id int NOT NULL AUTO_INCREMENT PRIMARY KEY,    FirstName varchar,    LastName varchar ); ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near ', LastName varchar )' at line 4You can correct the above error by providing the size for varchar data type like varchar(100). The same will fix the issue.Let’s fix it ... Read More

To use the reserved keyword ‘Key’, use the concept of the backtick symbol. Here, for our example, I am using the column name key which needs a backtick symbol around the column name.Let us first create a table −mysql> create table DemoTable (    `Key` int ); Query OK, 0 rows affected (0.67 sec)Insert some records in the table using insert command −mysql> insert into DemoTable values(100); Query OK, 1 row affected (0.16 sec) mysql> insert into DemoTable values(101); Query OK, 1 row affected (0.55 sec) mysql> insert into DemoTable values(110); Query OK, 1 row affected (0.28 sec) mysql> insert ... Read More

Let us first create a table −mysql> create table DemoTable (    Money DECIMAL(7, 2) ); Query OK, 0 rows affected (0.58 sec)Insert some records in the table using insert command −mysql> insert into DemoTable values(100.67); Query OK, 1 row affected (0.16 sec) mysql> insert into DemoTable values(199.33); Query OK, 1 row affected (0.12 sec) mysql> insert into DemoTable values(500); Query OK, 1 row affected (0.19 sec) mysql> insert into DemoTable values(400); Query OK, 1 row affected (0.14 sec) mysql> insert into DemoTable values(800); Query OK, 1 row affected (0.14 sec)Display all records from the table using select statement −mysql> ... Read More

For this, you can use GROUP BY HAVING clause. Let us first create a table −mysql> create table DemoTable (    Id int NOT NULL AUTO_INCREMENT PRIMARY KEY,    Value int ); Query OK, 0 rows affected (0.52 sec)Insert some records in the table using insert command −mysql> insert into DemoTable(Value) values(600); Query OK, 1 row affected (0.14 sec) mysql> insert into DemoTable(Value) values(600); Query OK, 1 row affected (0.14 sec) mysql> insert into DemoTable(Value) values(800); Query OK, 1 row affected (0.12 sec) mysql> insert into DemoTable(Value) values(800); Query OK, 1 row affected (0.09 sec)Display all records from the table ... Read More

For this, use JSON_OBJECTAGG(). Let us first create a table −mysql> create table DemoTable (    Id int,    FirstName varchar(100),    Age int ); Query OK, 0 rows affected (0.56 sec)Insert some records in the table using insert command −mysql> insert into DemoTable values(10, 'John', 23); Query OK, 1 row affected (0.18 sec) mysql> insert into DemoTable values(20, 'Carol', 21); Query OK, 1 row affected (0.13 sec) mysql> insert into DemoTable values(10, 'Sam', 24); Query OK, 1 row affected (0.15 sec) mysql> insert into DemoTable values(20, 'Chris', 20); Query OK, 1 row affected (0.13 sec)Display all records from the ... Read More

Let us first create a table −mysql> create table DemoTable (    Logouttime time ); Query OK, 0 rows affected (0.62 sec)Insert some records in the table using insert command −mysql> insert into DemoTable values('5:50:00'); Query OK, 1 row affected (0.15 sec) mysql> insert into DemoTable values('6:10:10'); Query OK, 1 row affected (0.17 sec) mysql> insert into DemoTable values('8:00:50'); Query OK, 1 row affected (0.14 sec)Display all records from the table using select statement −mysql> select *from DemoTable;This will produce the following output −+------------+ | Logouttime | +------------+ | 05:50:00 | | 06:10:10 | | 08:00:50 ... Read More

For this, you can use the aggregate function SUM(). Let us first create a table −mysql> create table DemoTable (    isMarried tinyint(1) ); Query OK, 0 rows affected (0.84 sec)Insert some records in the table using insert command −mysql> insert into DemoTable values(0); Query OK, 1 row affected (0.26 sec) mysql> insert into DemoTable values(1); Query OK, 1 row affected (0.11 sec) mysql> insert into DemoTable values(1); Query OK, 1 row affected (0.21 sec) mysql> insert into DemoTable values(0); Query OK, 1 row affected (0.20 sec) mysql> insert into DemoTable values(1); Query OK, 1 row affected (0.19 sec) mysql> ... Read More

Let’s say you have set dates in the VARCHAR format. Now if you want to update the format, then use the UPDATE command along with STR_TO_DATE(). The syntax is as follows −update yourTableName set yourColumnName=str_to_date(yourColumnName, '%m/%d/%Y');Let us first create a table −mysql> create table DemoTable (    DueDate varchar(100) ); Query OK, 0 rows affected (0.56 sec)Insert some records in the table using insert command −mysql> insert into DemoTable values('12/01/2019'); Query OK, 1 row affected (0.17 sec) mysql> insert into DemoTable values('01/31/2016'); Query OK, 1 row affected (0.16 sec) mysql> insert into DemoTable values('03/17/2018'); Query OK, 1 row affected (0.17 ... Read More

Let us first create a table −mysql> create table DemoTable (    isValidUser boolean ); Query OK, 0 rows affected (0.70 sec)Insert some records in the table using insert command −mysql> insert into DemoTable values(true); Query OK, 1 row affected (0.19 sec) mysql> insert into DemoTable values(false); Query OK, 1 row affected (0.07 sec) mysql> insert into DemoTable values(false); Query OK, 1 row affected (0.10 sec) mysql> insert into DemoTable values(true); Query OK, 1 row affected (0.11 sec) mysql> insert into DemoTable values(true); Query OK, 1 row affected (0.13 sec) mysql> insert into DemoTable values(true); Query OK, 1 row affected ... Read More