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Articles on Trending Technologies
Technical articles with clear explanations and examples
Perform MySQL delete under safe mode?
To delete under safe mode, you can use the below query −SET SQL_SAFE_UPDATES = 0;To understand the above query, let us create a table. The following is the query to create a table −mysql> create table SafeDeleteDemo −> ( −> Price int −> ); Query OK, 0 rows affected (0.50 sec)Insert some records in the table with the help of insert command. The query is as follows −mysql> insert into SafeDeleteDemo values(100); Query OK, 1 row affected (0.11 sec) mysql> insert into SafeDeleteDemo values(200); Query OK, 1 row affected (0.19 sec) mysql> insert into SafeDeleteDemo ...
Read MoreIn MySQL how to select the top 2 rows for each group?
To select the top 2 rows from each group, use the where condition with subquery. Let us create a table. The query to create a table is as follows:mysql> create table selectTop2FromEachGroup -> ( -> Name varchar(20), -> TotalScores int -> ); Query OK, 0 rows affected (0.80 sec)Now insert some records in the table using insert command. The query is as follows:mysql> insert into selectTop2FromEachGroup values('John', 32); Query OK, 1 row affected (0.38 sec) mysql> insert into selectTop2FromEachGroup values('John', 33); Query OK, 1 row affected (0.21 sec) mysql> insert into selectTop2FromEachGroup values('John', 34); Query OK, ...
Read MoreSplit the left part of a string by a separator string in MySQL?
You can use substring_index() function from MySQL to split the left part of a string. The syntax is as follows −SELECT yourColumnName1, .....N, SUBSTRING_INDEX(yourColumnName, ’yourSeperatorSymbol’, 1) as anyVariableName from yourTableName;The value 1 indicates that you can get left part of string. To check the above syntax, let us create a table. The query to create a table is as follows −mysql> create table LeftStringDemo -> ( -> Id int, -> Words varchar(100) -> ); Query OK, 0 rows affected (0.92 sec)Insert some records in the table using insert ...
Read MoreHow many different types of eclipses are there?
An Eclipse is formed when a celestial body is obscured by another. We know that eclipses occur when sun, moon, and earth align in a straight line. The Solar eclipse occurs when the moon comes in between the sun and the earth. The Lunar eclipse is formed when the earth blocks the way for the sunlight to reach the moon.Penumbra and AntumbraThe umbra is the innermost and darkest part of the shadow, which is the area when an observer can experience the eclipse completely. The Penumbra is the area in which only a portion of the light is obscured by ...
Read MoreCan MySQL automatically convert empty strings to NULL?
You need to use NULLIF() function from MySQL. The syntax is as follows:SELECT NULLIF(yourCoumnName, ’ ’) as anyVariableName from yourTableName;In the above syntax, if you compare empty string( ‘ ‘) to empty string( ‘ ‘), the result will always be NULL. However, if you compare with NULL to empty string( ‘ ‘) then also the result will always be NULL.To understand the above syntax, let us create a table. The query to create a table is as follows:mysql> create table ConvertEmptyStringToNULL -> ( -> Id int NOT NULL AUTO_INCREMENT, -> Name varchar(20), -> PRIMARY KEY(Id) ...
Read MoreHow to count distinct values in MySQL?
To count distinct values, you can use distinct in aggregate function count().The syntax is as follows −select count(distinct yourColumnName) as anyVariableName from yourTableName;To understand the above concept, let us create a table. The following is the query to create a table −mysql> create table DistinctDemo −> ( −> Name varchar(200) −> ); Query OK, 0 rows affected (0.58 sec)For our example, let us insert duplicate records in the table. The query to insert records is as follows −mysql> insert into DistinctDemo values('John'); Query OK, 1 row affected (0.15 sec) mysql> ...
Read MoreWhat is the difference between int and integer in MySQL?
The int is the synonym of integer in MySQL 5.0. Here is the demo display both int and integer internally represents int(11).Creating a table with int datatypemysql> create table IntDemo -> ( -> Id int -> ); Query OK, 0 rows affected (1.04 sec)Here is description of the table. The query is as followsmysql> desc IntDemo;The following is the output+-------+---------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +-------+---------+------+-----+---------+-------+ | Id | int(11) | YES | | NULL | | +-------+---------+------+-----+---------+-------+ 1 row in ...
Read MoreWhat is the best use of a smartphone?
A smartphone is the most common device often seen in the hands of people, starting from the small kids to a 60 years old man. What is so special about this gadget? Does it only make life easier? What are the additional benefits this gadget offers? Numerous questions come to the mind of the users when they are buying the smart phone for the first time.For some folks, these gadgets are nothing but an instrument of entertainment. For some, it is the way to communicate to people around the world; some use it as the camera, whereas some may use ...
Read MoreChanging Column in MySQL from int to double?
To change the column in MySQL from int to double you need to use ALTER TABLE command.The syntax is as follows:ALTER TABLE yourTableName modify column yourColumnName DOUBLE NOT NULL;If you want NULL value then remove NOT NULL from the above syntax. The syntax is as follows:ALTER TABLE yourTableName modify column yourColumnName DOUBLE;To understand the above syntax, let us create a table. The query to create a table is as follows:mysql> create table IntToDoubleDemo -> ( -> Id int NOT NULL AUTO_INCREMENT, -> Name varchar(10), -> CylinderVolume int, -> PRIMARY KEY(Id) -> ); Query OK, ...
Read MoreUsing group by on two fields and count in MySQL?
To implement GROUP BY on two fields and count, let us create a table. The following is the query to create a table −mysql> create table GroupByTwoFieldsDemo −> ( −> Id int, −> Name varchar(200) −> ); Query OK, 0 rows affected (0.53 sec)Let us insert some records in the table −mysql> insert into GroupByTwoFieldsDemo values(1, 'John'); Query OK, 1 row affected (0.15 sec) mysql> insert into GroupByTwoFieldsDemo values(10, 'Johnson'); Query OK, 1 row affected (0.16 sec) mysql> insert into GroupByTwoFieldsDemo values(9, 'Carol'); Query OK, 1 row affected (0.14 sec) mysql> insert into ...
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