MySQLi Articles - Page 323 of 341

As we know that CONCAT() function will return NULL if any of the argument of it is NULL. It means MySQL will return NULL if we pass column name, containing a NULL value, as one of the arguments of CONCAT() function. Following is an example of ‘Student’ table to explain it.ExampleIn this example, we are concatenating the values of two strings and at 5th row one, the value is NULL hence the concatenation result is also NULL.mysql> Select Name, Address, CONCAT(Name, ' Resident of ', Address)AS 'Detail of Student' from Student; +---------+---------+---------------------------+ | Name    | Address | Detail ... Read More

Suppose from the table ‘Student’ we want to concatenate the values of columns, ‘Name’, ‘Address’ and ‘Columns’, based on the condition that is also a concatenation of values from columns, ’Name’, ‘Subject’, provided in WHERE clause with the help of CONCAT() function. We can use the following query to give the output −mysql> Select CONCAT(Name, ' ', 'Resident of', ' ', Address, ' ', 'is', ' ', 'Studying', ' ', Subject)AS 'Detail of Student' from Student WHERE CONCAT(Name, Subject) = "AaravHistory"; +----------------------------------------------+ | Detail of Student                            | ... Read More

We can use CONCAT() function to combine the values of two or more columns. In this case, the arguments of the CONCAT() functions would be the name of the columns. For example, suppose we have a table named ‘Student’ and we want the name and address of the student collectively in one column then the following query can be written −mysql> Select Id, Name, Address, CONCAT(ID, ', ', Name, ', ', Address)AS 'ID, Name, Address' from Student; +------+---------+---------+--------------------+ | Id   | Name    | Address | ID, Name, Address  | +------+---------+---------+--------------------+ | 1    | Gaurav  | Delhi   ... Read More

MySQL allows us to pass only one argument to the CONCAT() function. In this case, MySQL returns the same argument as output. Following example will exhibit it −Examplemysql> Select Concat('Delhi'); +-----------------+ | Concat('Delhi') | +-----------------+ | Delhi           | +-----------------+ 1 row in set (0.00 sec)

When BIN() string function is used with WHERE clause, the output returns by it will depend upon the condition given in WHERE clause. In this case, we must have to use binary value in WHERE clause. For example, suppose we have a table named ‘Student’ and we want to get only those rows where the binary value of column ‘id’ is higher than 1010, then we can write following query −mysql> Select *, Bin(id) from student where BIN(id) > 1010 ; +------+---------+---------+-----------+---------+ | Id   | Name    | Address | Subject   | Bin(id) | +------+---------+---------+-----------+---------+ | 15   ... Read More

Last_Insert_Id() MySQL function is used to find out which sequence number was assigned recently by AUTO_INCREMENT.Examplemysql> Create table Employee(Id INT PRIMARY KEY NOT NULL AUTO_INCREMENT, Name Varchar(5)); Query OK, 0 rows affected (0.13 sec) mysql> Insert into Employee(Name) Values('Harvinder'); Query OK, 1 row affected (0.06 sec) mysql> Insert into Employee(Name) Values('Suresh'); Query OK, 1 row affected (0.07 sec) mysql> Select* from Employee; +----+---------+ | Id | Name    | +----+---------+ | 1  |Harvinder| | 2  | Suresh  | +----+---------+ 2 rows in set (0.00 sec) mysql> Select Last_insert_id(); +------------------+ | Last_insert_id() | +------------------+ |                2 | +------------------+ 1 row in set (0.00 sec)

With the help of the following command we can force MySQL out of TRADITIONAL mode −mysql> Set SQL_MODE =''; Query OK, 0 rows affected (0.00 sec)

In case of enabled SQL strict mode, subtraction between integers value in which one is of UNSIGNED type will produce an unsigned result by default. But MySQL produces an error if the result is a negative one. It can be observed with the following example −mysql> SET sql_mode = ''; Query OK, 0 rows affected (0.00 sec) mysql> Select CAST(0 AS UNSIGNED) -1; ERROR 1690 (22003): BIGINT UNSIGNED value is out of range in '(cast(0 as unsigned) - 1)'The error after the query above shows that it is an overflow after numeric arithmetic expression.Now, it can be handled with ... Read More

MySQL CAST can handle overflow occurs during numerical expression assessment. Suppose if numeric expression evaluation produces overflow then MySQL reflects an error message. Now to handle this overflow we can change that numeric value to UNSIGNED with the help of CAST.For example on adding 1 to BIGINT maximum value, MySQL produce an error due to overflow as follows −mysql> Select 9223372036854775807 + 1; ERROR 1690 (22003): BIGINT value is out of range in '(9223372036854775807+1)'Now, with the help of CAST, MySQL handles this kind of overflow as follows:mysql> Select CAST(9223372036854775807 AS UNSIGNED) +1; +------------------------------------------+ | CAST(9223372036854775807 AS UNSIGNED) +1 | +------------------------------------------+ | 9223372036854775808                      | +------------------------------------------+ 1 row in set (0.07 sec)

As we know that MySQL will produce an error if overflow occurs during the assessment of numeric expressions. For example, the largest signed BIGNT is 9223372036854775807, so the following expression will produce an error −mysql> Select 9223372036854775807 + 1; ERROR 1690 (22003): BIGINT value is out of range in '(9223372036854775807+1)'MySQL can handle such kind of overflows in following ways:BY CONVERTING VALUE TO UNSIGNEDMySQL enables such kind of operations by converting the values to unsigned as follows −mysql> Select CAST(9223372036854775807 AS UNSIGNED) +1; +------------------------------------------+ | CAST(9223372036854775807 AS UNSIGNED) +1 | +------------------------------------------+ |                   ... Read More