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Database Articles
Page 250 of 547
How to check if a column exist in a MySQL table?
To understand whether a column exist or not, we have the following approaches −With the help of DESC commandUsing SHOW commandFirstly, we will create a table with columns −mysql> CREATE table ColumnExistDemo -> ( -> UniqueId int, -> UniqueName varchar(200), -> UniqueAddress varchar(200) -> ); Query OK, 0 rows affected (0.57 sec)In the first approach, we will get the entire column name with meaningful information. The syntax is as follows −DESC yourTableName; Let us apply the above query to check whether the column name exists or not. However, this approach is not good since it display all the columns.mysql> DESC ...
Read MoreCan a number be used to name a MySQL table column?
Yes, we can include a number for column name in MySQL. We need to use the symbol backtick, which is as follows( ` `)To understand, we will make a table with the help of CREATE command. Let us create a table −mysql> CREATE table NumberColumnDemo -> ( -> `123` varchar(100) -> ); Query OK, 0 rows affected (0.51 sec)Above, I have created a column name as a number with the help of backtick symbol.Now, we can check the same by inserting records with the help of INSERT command. Let us insert a record, which is as follows −mysql> INSERT into ...
Read MoreWhich one should I use? The datetime or timestamp data type in MySQL?
Timestamp is a data type in MySQL and works for different time zone. It is also used for date and time purpose To understand the concept, we need to create a table.Creating a tablemysql> CREATE table TimeStampDemo -> ( -> MyDataTime timestamp -> ); Query OK, 0 rows affected (0.57 sec)After creating the table, we will insert a record with the help of INSERT command.Inserting recordsmysql> INSERT into TimeStampDemo values (now()); Query OK, 1 row affected (0.12 sec)After inserting a record, we can display the records with the help of SELECT statement.Displaying recordsmysql> SELECT * from TimeStampDemo; After executing the ...
Read MoreWhat is ROW_NUMBER() in MySQL?
Row_NUMBER() included from MySQL version 8.0. It is a type of window function. This can be used to assign a sequence number for rows. To understand, create a table with the help of CREATE pcommand −Creating a tablemysql> CREATE table rowNumberDemo -> ( -> FirstName varchar(100) -> ); Query OK, 0 rows affected (0.92 sec)Inserting recordsmysql> INSERT into rowNumberDemo values('john'); Query OK, 1 row affected (0.17 sec) mysql> INSERT into rowNumberDemo values('john'); Query OK, 1 row affected (0.29 sec) mysql> INSERT into rowNumberDemo values('Bob'); Query OK, 1 row affected (0.13 sec) mysql> INSERT into rowNumberDemo values('Smith'); Query ...
Read MoreHow to convert an MySQL database characterset and collation to UTF-8?
Firstly, we will check which MySQL version is currently being used with the help of version() function −The query is as follows −mysql> SELECT version();The following is the output+-----------+ | version() | +-----------+ | 8.0.12 | +-----------+ 1 row in set (0.00 sec)As you can see in the above output, version 8.0.12 is being used. Now, we can check the current character encoding using the following syntax −SELECT CCSA.character_set_name FROM information_schema.`TABLES`T, information_schema.`COLLATION_CHARACTER_SET_APPLICABILITY` CCSA WHERE CCSA.collation_name -> =T.table_collation AND T.table_schema = "yourDatabaseName" AND T.table_name = "yourTableName";Apply the above query −mysql> SELECT CCSA.character_set_name FROM information_schema.`TABLES`T, information_schema.`COLLATION_CHARACTER_SET_APPLICABILITY` CCSA WHERE CCSA.collation_name ...
Read MoreHow to save time in milliseconds in MySQL?
To save time in milliseconds, we can use now(3) function because “milli 3” can be used for te same purpose. Firstly, I will create a table with the help of CREATE command −mysql> CREATE table MilliSecondDemo -> ( -> MyTimeInMillSec datetime(3) -> ); Query OK, 0 rows affected (0.70 sec)Inserting record into the table −mysql> INSERT into MilliSecondDemo values(now(3)); Query OK, 1 row affected (0.98 sec)Let us now view the table records −mysql> SELECT * from MilliSecondDemo; The following is the output+-------------------------+ | MyTimeInMillSec | +-------------------------+ | 2018-10-08 15:19:50.202 | +-------------------------+ 1 row in set (0.00 sec)
Read MoreHow to measure actual MySQL query time?
To measure actual MySQL query time, we can use the concept of profiling that must be set to 1 before executing the query.The order must be like this.Set profiling to 1 Then execute query Then show profilesNow, I am applying the above order to get the actual MySQL query time −mysql> SET profiling = 1; Query OK, 0 rows affected, 1 warning (0.00 sec)After that I am executing the following query −mysql> SELECT * from MilliSecondDemo; The following is the output+-------------------------+ | MyTimeInMillSec | +-------------------------+ | 2018-10-08 15:19:50.202 | +-------------------------+ 1 row ...
Read MoreHow to use Straight Join in MySQL?
The straight join in MySQL works like inner join or join. This means that it returns only the matching rows. Firstly, we need to understand Straight join in MySQL. For that, we need to create two tables and relate both the tables with foreign key constraints.Here is the first tablemysql> CREATE table ForeignTableDemo -> ( -> Id int, -> Name varchar(100), -> FK int -> ); Query OK, 0 rows affected (0.47 sec)Here is the second table −mysql> CREATE table PrimaryTableDemo -> ( -> FK int, -> Address varchar(100), -> primary key(FK) -> ); Query OK, 0 rows affected (0.47 ...
Read MoreHow to display all the tables in MySQL with a storage engine?
We can display all the tables with the help of the WHERE clause. The syntax for that is as follows −SELECT table_name FROM INFORMATION_SCHEMA.TABLES WHERE engine = 'InnoDB';Now, the above syntax is applied to the given query −mysql> SELECT * from INFORMATION_SCHEMA.TABLES WHERE engine = 'InnoDB';The following is the output obtained −+---------------+--------------+---------------------------+------------+--------+---------+------------+------------+----------------+-------------+-----------------+--------------+-----------+----------------+---------------------+---------------------+------------+--------------------+----------+---------------------------------------+-----------------------------------------+ | TABLE_CATALOG | TABLE_SCHEMA | TABLE_NAME | TABLE_TYPE | ENGINE | VERSION | ROW_FORMAT | TABLE_ROWS | AVG_ROW_LENGTH | DATA_LENGTH | MAX_DATA_LENGTH | INDEX_LENGTH | DATA_FREE | AUTO_INCREMENT | CREATE_TIME | UPDATE_TIME | CHECK_TIME | TABLE_COLLATION | CHECKSUM | CREATE_OPTIONS | TABLE_COMMENT | +---------------+--------------+---------------------------+------------+--------+---------+------------+------------+----------------+-------------+-----------------+--------------+-----------+----------------+---------------------+---------------------+------------+--------------------+----------+---------------------------------------+-----------------------------------------+ | def | mysql ...
Read MorePagination using MySQL LIMIT, OFFSET?
Firstly, we need to create a table with some records, then we will use pagination with the help of limit and offset.Creating a table with the help of CREATE command. The query is as follows −mysql> CREATE table limitoffsetDemo -> ( -> id int, -> FisrtName varchar(200) -> ); Query OK, 0 rows affected (0.45 sec)After creating a table, we will insert records with the help of INSERT command.Inserting recordsmysql> INSERT into limitoffsetDemo values(1, 'John'); Query OK, 1 row affected (0.11 sec) mysql> INSERT into limitoffsetDemo values(2, 'Bob'); Query OK, 1 row affected (0.16 sec) mysql> INSERT into ...
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