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MySQLi Articles
Page 84 of 341
What MySQL would return if we refer a user variable which is not assigned any value explicitly?
In case, when we refer a user variable which is not assigned any value explicitly, MySQL would return NULL. In other words, its value would be NULL. Following example would illustrate it −mysql> Select @X, @Y, @Z, @S, @G; +------+-------+----------+------+------+ | @X | @Y | @Z | @S | @G | +------+-------+----------+------+------+ | Ram | Shyam | Students | 5000 | NULL | +------+-------+----------+------+------+ 1 row in set (0.00 sec)We can see from the above result set that @X, @Y, @Z and @S has been assigned values explicitly and they returned the values ...
Read MoreWhat happens if I will assign a value to a MySQL user variable using a statement that returns multiple rows?
In case, if we will assign a value to a user variable using a statement that returns multiple rows then the value from the last row would be saved in that user variable because user variables can save the only single value. Following the example, in which we are using data from table ‘Tender’, will exhibit it −Examplemysql> select * from Tender; +----+---------------+--------------+ | Sr | CompanyName | Tender_value | +----+---------------+--------------+ | 1 | Abc Corp. | 250.369003 | | 2 | Khaitan Corp. | 265.588989 | | 3 | Singla group. | 220.255997 ...
Read MoreHow can we use SET statement to assign a SELECT result to a MySQL user variable?
For using the SET statement to assign a SELECT result to a user variable we need to write the SELECT statement as a subquery within parentheses. The condition is that the SELECT statement must have to return a single value. To make it understand we are using the data from ‘Tender’ table which is as follows −mysql> select * from Tender; +----+---------------+--------------+ | Sr | CompanyName | Tender_value | +----+---------------+--------------+ | 1 | Abc Corp. | 250.369003 | | 2 | Khaitan Corp. | 265.588989 | | 3 | Singla group. | 220.255997 | ...
Read MoreHow does MySQL QUOTE() function work with comparison values?
When QUOTE() function used with WHERE clause then the output depends upon the comparison values returned by WHERE clause. Following example will exhibit it −Examplemysql> Select Name, ID, QUOTE(Subject)AS Subject from Student WHERE Subject = 'History'; +-------+------+-----------+ | Name | ID | Subject | +-------+------+-----------+ | Aarav | 2 | 'History' | +-------+------+-----------+ 1 row in set (0.00 sec)
Read MoreHow can we take a backup of the single database by using mysqldump client program?
By using mysqldump client program we can take the backup of a database into a file having the extension ‘.sql’. it can be understood with the help of following example −ExampleIn this example, with the help of mysqldump client program, we are taking the backup of a database named ‘tutorials’ in a file named ‘tutorials.sql’. The following command will do this −C:\mysql\bin>mysqldump -u root tutorials > tutorials.sqlThe above command will create a file named ‘turorials.sql’ in the bin folder of MySQL. This file will contain drop table, create a table and insert command for all the tables in the tutorials ...
Read MoreHow can we take a backup of multiple databases by using mysqldump client program?
By using mysql dump client program we can take the backup of multiple databases into a file having the extension ‘.sql’. It can be understood with the help of the following example −ExampleIn this example, with the help of mysql dump client program, we are taking the backup of two databases named ‘tutorials’ and ‘query1’ in a file named ‘tutorials_query1.sql’. The following command will do this −C:\mysql\bin>mysqldump -u root --databases tutorials query1 > tutorials_query1.sqlThe above command will create a file named tutorials_query1.sql which have the dump information of both the databases named tutorials and query1.
Read MoreHow can I restore a file created by mysqldump?
Suppose if we want to restore a file that has been created by mysqldump then we can restore in an existing database or in a new database after creating it. Then with the help of SOURCE statement, we can restore it. We can illustrate it by an example:ExampleIn this example, we are restoring the table named student_info.sql which has been dumped. It was basically in the database name ‘query’. Now we will restore it into a database named ‘tutorials’.mysql> Use Tutorials; Database changed mysql> SOURCE student_info.sql; Query OK, 0 rows affected (0.00 sec) Query OK, 0 rows affected ...
Read MoreHow can we upload data into MySQL tables by using mysqlimport?
For uploading the data into MySQL tables by using mysqlimport we need to follow following steps −Step-1 − Creating the tablefirst of all, we need to have a table in which we want to upload the data. We can use CREATE TABLE statement for creating a MySQL table. For example, we created a table named ‘student_tbl’ as follows −mysql> DESCRIBE Student_tbl; +--------+-------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +--------+-------------+------+-----+---------+-------+ | RollNo | int(11) | YES | | NULL | | | ...
Read MoreHow can we upload data into multiple MySQL tables by using mysqlimport?
With the help of mysqlimport we can upload data into multiple MySQL tables. It is illustrated in the example below −ExampleSuppose we want to upload the following data from two data files namely student1_tbl.txt −1 Saurav 11th 2 Sahil 11th 3 Digvijay 11thAnd House.txt1 Furniture 2 Television 3 RefrigeratorFollowings are MySQL tables into which we want to upload the above data −mysql> DESCRIBE Student1_tbl; +--------+-------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +--------+-------------+------+-----+---------+-------+ | RollNo | int(11) ...
Read MoreIn what cases, we cannot use MySQL TRIM() function?
Actually for using MySQL TRIM() function we must have to know the string which we want to trim from the original string. This becomes the major drawback of TRIM() in the cases where we want to trim the strings having different values. For example, suppose we want to get the output after trimming the last two characters from the strings but every string is having different characters at last two places.Examplemysql> Select * from Employee; +------+----------------+------------+-----------------+ | Id | Name | Address | Department | +------+----------------+------------+-----------------+ | 100 | Raman ...
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