For this, use LENGTH(), since if the length is 0 that would mean the string is empty. After finding, you can set it to NULL using the SET clause in the UPDATE command. Let us first create a table −mysql> create table DemoTable (    Name varchar(50) ); Query OK, 0 rows affected (0.68 sec)Insert some records in the table using insert command −mysql> insert into DemoTable values('Chris'); Query OK, 1 row affected (0.18 sec) mysql> insert into DemoTable values(''); Query OK, 1 row affected (0.14 sec) mysql> insert into DemoTable values('David'); Query OK, 1 row affected (0.12 sec) mysql> ... Read More

Let us first create a table −mysql> create table DemoTable (    Id int ); Query OK, 0 rows affected (0.71 sec)Insert some records in the table using insert command −mysql> insert into DemoTable values(100); Query OK, 1 row affected (0.31 sec) mysql> insert into DemoTable values(101); Query OK, 1 row affected (0.26 sec) mysql> insert into DemoTable values(102); Query OK, 1 row affected (0.11 sec) mysql> insert into DemoTable values(103); Query OK, 1 row affected (0.64 sec) mysql> insert into DemoTable values(104); Query OK, 1 row affected (0.12 sec) mysql> insert into DemoTable values(105); Query OK, 1 row affected ... Read More

To avoid using the BETWEEN clause, you can use the AND to fetch the values between a range. Let us first create a table −mysql> create table DemoTable (    Number int ); Query OK, 0 rows affected (0.62 sec)Insert some records in the table using insert command −mysql> insert into DemoTable values(10); Query OK, 1 row affected (0.14 sec) mysql> insert into DemoTable values(20); Query OK, 1 row affected (0.24 sec) mysql> insert into DemoTable values(60); Query OK, 1 row affected (0.10 sec) mysql> insert into DemoTable values(100); Query OK, 1 row affected (0.07 sec) mysql> insert into DemoTable ... Read More

To fetch the first alphabet from the strings, use LEFT(). This method allows you to return characters from the left of the string.Let us first see an example and create a table −mysql> create table DemoTable (    Id int NOT NULL AUTO_INCREMENT PRIMARY KEY,    FirstName varchar(100) ); Query OK, 0 rows affected (1.03 sec)Insert some records in the table using insert command −mysql> insert into DemoTable(FirstName) values('John'); Query OK, 1 row affected (0.11 sec) mysql> insert into DemoTable(FirstName) values('Adam'); Query OK, 1 row affected (0.10 sec) mysql> insert into DemoTable(FirstName) values('Jace'); Query OK, 1 row affected (0.16 sec) ... Read More

To change the column name, use the AS keyword after the column name. Let us first create a table −mysql> create table DemoTable (    Id int,    StudentFirstNameInCollege varchar(100) ); Query OK, 0 rows affected (0.68 sec)Insert some records in the table using insert command −mysql> insert into DemoTable values(100, 'Chris'); Query OK, 1 row affected (0.19 sec) mysql> insert into DemoTable values(101, 'Bob'); Query OK, 1 row affected (0.21 sec) mysql> insert into DemoTable values(102, 'David'); Query OK, 1 row affected (0.21 sec)Display all records from the table using select statement −mysql> select *from DemoTable;This will produce the ... Read More

For this, you can use the ORDER BY clause. Let us first create a table −mysql> create table DemoTable (    Name varchar(40),    Score int ); Query OK, 0 rows affected (1.11 sec)Insert some records in the table using insert command −mysql> insert into DemoTable values('Chris', 45); Query OK, 1 row affected (0.26 sec) mysql> insert into DemoTable values('Bob', 98); Query OK, 1 row affected (0.10 sec) mysql> insert into DemoTable values('David', 78); Query OK, 1 row affected (0.17 sec) mysql> insert into DemoTable values('Mike', 96); Query OK, 1 row affected (0.14 sec) mysql> insert into DemoTable values('Carol', 43); ... Read More

You can use REPLACE INTO that works like DELETE + INSERT. Let us first create a table −mysql> create table DemoTable (    Id int,    FirstName varchar(50) ); Query OK, 0 rows affected (0.60 sec)Following is the query to create a unique index −mysql> alter table DemoTable add unique id_index(Id); Query OK, 0 rows affected (0.41 sec) Records: 0 Duplicates: 0 Warnings: 0Insert some records in the table using insert command. Since we have added duplicate records, the new record gets added i.e. replaced with the same Id with the previous record −mysql> replace into DemoTable values(100, 'Chris'); Query ... Read More

To find the highest and lowest from two tables, use MAX() and MIN(). Since the results are to be displayed from two tables, you need to use UNION. Let us first create a table −mysql> create table DemoTable1 (    UniqueId int NOT NULL AUTO_INCREMENT PRIMARY KEY,    Score1 int ); Query OK, 0 rows affected (0.76 sec)Insert some records in the table using insert command −mysql> insert into DemoTable1(Score1) values(56); Query OK, 1 row affected (0.14 sec) mysql> insert into DemoTable1(Score1) values(76); Query OK, 1 row affected (0.12 sec) mysql> insert into DemoTable1(Score1) values(65); Query OK, 1 row affected ... Read More

If your first column is AUTO_INCREMENT, then you can skip the column and place the value NULL. Let us first create a table −mysql> create table DemoTable (    StudentId int NOT NULL AUTO_INCREMENT PRIMARY KEY,    StudentFirstName varchar(100),    StudentAge int ); Query OK, 0 rows affected (0.60 sec)Insert some records in the table using insert command. Here, we have skipped the first column, since it is AUTO_INCREMENT −mysql> insert into DemoTable values(NULL, 'Robert', 21); Query OK, 1 row affected (0.21 sec) mysql> insert into DemoTable values(NULL, 'Sam', 22); Query OK, 1 row affected (0.18 sec) mysql> insert into ... Read More

To optimize many SELECTs, use it once and apply IN() to fetch multiple values. Let us first create a table −mysql> create table DemoTable (    Id int,    Name varchar(100),    Age int ); Query OK, 0 rows affected (0.77 sec)Insert some records in the table using insert command −mysql> insert into DemoTable values(1, 'Chris', 23); Query OK, 1 row affected (0.39 sec) mysql> insert into DemoTable values(2, 'David', 21); Query OK, 1 row affected (0.56 sec) mysql> insert into DemoTable values(3, 'Mike', 24); Query OK, 1 row affected (0.28 sec) mysql> insert into DemoTable values(4, 'Robert', 22); Query ... Read More