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Articles by seetha
Page 4 of 6
When a MySQL arithmetic expression returns NULL?
As we know that a NULL is not a value and it is also not the same as zero. MySQL arithmetic expression returns NULL if we will use NULL in it. It can be understood with the help of the following example −Examplemysql> Select 100*NULL; +----------+ | 100*NULL | +----------+ | NULL | +----------+ 1 row in set (0.00 sec) mysql> Select 100+NULL; +----------+ | 100+NULL | +----------+ | NULL | +----------+ 1 row in set (0.00 sec)From the above example, it can be observed that if we will use NULL in an arithmetic expression then the result would be NULL itself.
Read MoreHow it is possible to insert a zero or an empty string into a MySQL column which is defined as NOT NULL?
Declaring a column ‘NOT NULL’ means that this column would not accept NULL values but zero (0) and an empty string is itself a value. Hence there would be no issue if we want to insert zero or an empty string into a MySQL column which is defined as NOT NULL. Following comparisons of 0 and empty string with NULL would make it clear −mysql> Select 0 IS NULL, 0 IS NOT NULL; +-----------+---------------+ | 0 IS NULL | 0 IS NOT NULL | +-----------+---------------+ | 0 | 1 | ...
Read MoreHow can we sort multiple columns in a single query?
We can sort multiple columns in a single query by giving more than one column name with ORDER BY Clause. The syntax of the above is as follows −SyntaxSelect Col1, Col2, … from table_name ORDER BY Col1, Col2, …ExampleSuppose we want to sort the table named ‘Student’ by columns ‘Name’ and ‘RollNo’ both then we can write the single query for this as follows −mysql> Select Name, RollNo from student order by name, rollno; +--------+--------+ | name | rollno | +--------+--------+ | Aarav | 150 | | Aryan | 165 ...
Read MoreHow can we delete a MySQL stored function from the database?
If we have ALTER ROUTINE privileges then with the help of DROP FUNCTION statement, we can delete a MySQL stored function. Its syntax can be as follows −SyntaxDROP FUNCTION [IF EXISTS] function_nameHere function_name is the name of the function which we want to delete from our database.Examplemysql> DROP FUNCTION if exists Hello1; Query OK, 0 rows affected (0.70 sec)Now after deleting the function, check for the CREATE FUNCTION statement and we will get the error as follows −mysql> SHOW CREATE FUNCTION Hello1; ERROR 1305 (42000): Function Hello1 does not exist.
Read MoreDoes MySQL preserve the environment at the time the stored procedure created?
Actually, MySQL preserves the environment at the time the stored procedure is created. It can be understood with the help of following the example in which we are using two bars for concatenating strings. This is only legal while SQL mode is ansi. But if we change the SQL mode to non-ansi, the procedure still works as if the original setting is still true.Examplemysql> Set sql_mode = 'ansi'// Query OK, 0 rows affected, 1 warning (0.14 sec) mysql> Create Procedure Con_string() -> SELECT 'a'||'b'// Query OK, 0 rows affected (0.12 sec) mysql> Call Con_string (); +----------+ | ...
Read MoreHow can I create a stored procedure to select values on the basis of some conditions from a MySQL table?
We can create a stored procedure with IN and OUT operators to SELECT records, based on some conditions, from MySQL table. To make it understand we are taking an example of a table named ‘student_info’ having the following data −mysql> Select * from student_info; +------+---------+------------+------------+ | id | Name | Address | Subject | +------+---------+------------+------------+ | 101 | YashPal | Amritsar | History | | 105 | Gaurav | Jaipur | Literature | | 110 | ...
Read MoreHow can we create a MySQL user account by omitting the hostname?
If we omit the hostname part of the user account, MySQL will accept it and allow the user to connect from any host. Its syntax would be as follows −Use mysql; CREATE USER user_name IDENTIFIED BY password;Here, user_name is the name of the user we wish to take account of.Password is the password we wish to make for user_account. With the help of this password, MySQL server will identify this user.ExampleIn the given example we are creating a user ‘REMOTE’ by omitting the host name.mysql> CREATE USER remote identified by 'password123'; Query OK, 0 rows affected (0.00 sec)The user ‘Remote’ can ...
Read MoreHow can we distinguish between MySQL CROSS JOIN and INNER JOIN?
We can distinguish between MySQL CROSS JOIN and INNER JOIN only on the basis of join-predicate i.e. the condition specified. While writing the query for INNER JOIN we need to specify the condition but in contrast, we do not need to specify the condition while writing a query for CROSS JOIN. To understand it, we are taking the example of two tables named tbl_1 and tbl_2 which are having following data −mysql> Select * from tbl_1; +----+--------+ | Id | Name | +----+--------+ | 1 | Gaurav | | 2 | Rahul | | 3 | ...
Read MoreWhat is the similarity between prepared statements and MySQL user variables?
As we know that MySQL user variables are specific to client connection within which they are used and exist only for the duration of that connection. When a connection ends, all its user variables are lost. Similarly, the prepared statements also exist only for the duration of the session in which it is created and it is visible to the session in which it is created. When a session ends, all the prepared statements for that session are discarded.Another similarity is that prepared statements are also not case-sensitive like MySQL user variables. For example, stmt11 and STMT11 both are same ...
Read MoreHow can we MySQL LOAD DATA INFILE statement with 'ENCLOSED BY' option to import data from text file into MySQL table?
Sometimes the input text files have the text fields enclosed by double quotes and to import data from such kind of files we need to use the ‘ENCLOSED BY’ option with LOAD DATA INFILE statement. We are considering the following example to make it understand −ExampleFollowings are the comma-separated values in A.txt file −100, ”Ram”, ”INDIA”, 25000 101, ”Mohan”, ”INDIA”, 28000We want to import this data into the following file named employee2_tbl −mysql> Create table employee2_tbl(Id Int, Name Varchar(20), Country Varchar(20), Salary Int); Query OK, 0 rows affected (0.1 sec)Now, the transfer of data from a file to a ...
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