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Articles by George John
Page 66 of 79
MySQL query to get the count of rows in which two or more specified values appear?
To get the count of rows in which two or more specified values appear, let us first create a sample table:mysql> create table specifiedValuesDemo -> ( -> Value int, -> Value2 int, -> Value3 int -> ); Query OK, 0 rows affected (0.60 sec)Following is the query to insert some records in the table using insert command:mysql> insert into specifiedValuesDemo values(10, 15, 20); Query OK, 1 row affected (0.17 sec) mysql> insert into specifiedValuesDemo values(40, 10, 20); Query OK, 1 row affected (0.16 sec) ...
Read MoreSort by character length in MySQL
To sort by character length in MySQL use the ORDER BY LENGTH(). Let us first create a table:mysql> create table orderingAADemo -> ( -> Value varchar(100) -> ); Query OK, 0 rows affected (1.30 sec)Following is the query to insert some records in the table using insert command:mysql> insert into orderingAADemo values('A'); Query OK, 1 row affected (0.12 sec) mysql> insert into orderingAADemo values('B'); Query OK, 1 row affected (0.13 sec) mysql> insert into orderingAADemo values('AA'); Query OK, 1 row affected (0.20 sec) mysql> insert into orderingAADemo values('C'); Query OK, 1 row affected (0.12 ...
Read MoreHow to convert bool to int in MySQL?
To convert bool to int in MySQL, you can use CAST(). Let us first create a table:mysql> create table convertBoolToIntDemo -> ( -> isYoung bool -> ); Query OK, 0 rows affected (0.69 sec)Following is the query to insert some records in the table using insert command:mysql> insert into convertBoolToIntDemo values(true); Query OK, 1 row affected (0.18 sec) mysql> insert into convertBoolToIntDemo values(false); Query OK, 1 row affected (0.09 sec) mysql> insert into convertBoolToIntDemo values(true); Query OK, 1 row affected (0.15 sec) mysql> insert into convertBoolToIntDemo values(false); Query ...
Read MoreTotal number of fields in all tables in database?
To get total number of fields in all tables in database, you can use information_schema.columns along with aggregate function count(*).We are using ‘sample’ database which consists of a lot of tables with fields. Following is the query to get total number of fields in all tables in database:mysql> SELECT COUNT(*) AS TOTAL_NUMBER_OF_FIELDS -> FROM INFORMATION_SCHEMA.COLUMNS -> WHERE TABLE_SCHEMA = 'sample';This will produce the following output+------------------------+ | TOTAL_NUMBER_OF_FIELDS | +------------------------+ | 796 | +------------------------+ 1 row in set (0.04 sec)Now, let us check another database ‘test’. Following is the query ...
Read MoreHow to change a primary key in MySQL to auto_increment?
To change a primary key to auto_increment, you can use MODIFY command. Let us first create a table.mysql> create table changePrimaryKeyInAutoIncrement -> ( -> StudentId int not null primary key, -> StudentName varchar(100), -> StudentAge int, -> StudentAddress varchar(100) -> ); Query OK, 0 rows affected (0.63 sec)Let us now check the description of table using desc command:mysql> desc changePrimaryKeyInAutoIncrement;This will produce the following output+----------------+--------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +----------------+--------------+------+-----+---------+-------+ | StudentId | int(11) ...
Read MoreCount value for multiple columns in MySQL?
To count value for multiple columns, use the CASE statement. Let us first create a table::mysql> create table countValueMultipleColumnsDemo -> ( -> Value1 int, -> Value2 int, -> Value3 int -> ); Query OK, 0 rows affected (0.62 sec)Following is the query to insert some records in the table using insert command:mysql> insert into countValueMultipleColumnsDemo values(10, 15, 10); Query OK, 1 row affected (0.15 sec) mysql> insert into countValueMultipleColumnsDemo values(20, 30, 10); Query OK, 1 row affected (0.14 sec) mysql> insert into countValueMultipleColumnsDemo values(40, 10, 60); Query OK, 1 row affected (0.18 sec)Following ...
Read MoreC++ Program to Check if an UnDirected Graph is a Tree or Not Using DFS
A graph is a tree if it does not contain any cycle. This is a C++ program to check whether an undirected graph is tree or not.AlgorithmBegin function cyclicUtil() : A) Mark the current node as visited. B) Recur for all the vertices adjacent to this vertex. C) If an adjacent is not visited, then recur for that adjacent. D) If an adjacent is visited and not parent of current vertex, then there is a cycle. End Begin function cyclic(): A) Mark all the vertices as not visited and not part of recursion stack. ...
Read MoreIn a MySQL schema, what is the meaning of "AUTO_INCREMENT=3
In MySQL, AUTO_INCREMENT=3 tells that the inserted record will start from 3 not the default 1. Let us first create a sample table and set auto increment to 3:mysql> create table Auto_incrementDemo -> ( -> Id int NOT NULL AUTO_INCREMENT PRIMARY KEY, -> Name varchar(20) -> )AUTO_INCREMENT=3; Query OK, 0 rows affected (0.52 sec)Following is the query to insert some records in the table using insert command:mysql> INSERT INTO Auto_incrementDemo(Name) values('John'); Query OK, 1 row affected (0.12 sec) mysql> INSERT INTO Auto_incrementDemo(Name) values('Larry'); Query OK, 1 row affected (0.15 sec) mysql> INSERT INTO Auto_incrementDemo(Name) ...
Read MoreCan MySQL concatenate strings with ||?
Yes, you can concatenate strings with || in MySQL with the help of sql_mode. Set the sql_mode to PIPES_AS_CONCAT.The syntax is as followsset sql_mode=PIPES_AS_CONCAT;The following is the syntax to concat with the help of ||.SELECT ‘yourValue' || yourColumName AS anyAliasName FROM yourTableName;To understand the above syntax, let us create a table. The query to create a table is as followsmysql> create table PipeConcatDemo - > ( - > Name varchar(20) - > ); Query OK, 0 rows affected (0.93 sec)Insert some records in the table using insert command.The query is as followsmysql> insert into PipeConcatDemo values('Larry'); Query ...
Read MoreMySQL query to select one specific row and another random row?
To select one specific row and another random row, you can use ORDER BY and RAND(). Let us first create a sample table:mysql> create table oneSpecificRowAndOtherRandom -> ( -> Id int NOT NULL AUTO_INCREMENT PRIMARY KEY, -> Name varchar(20) -> ); Query OK, 0 rows affected (0.72 sec)Following is the query to insert some records in the table using insert command:mysql> insert into oneSpecificRowAndOtherRandom(Name) values('Larry'); Query OK, 1 row affected (0.56 sec) mysql> insert into oneSpecificRowAndOtherRandom(Name) values('Sam'); Query OK, 1 row affected (0.13 sec) mysql> insert into oneSpecificRowAndOtherRandom(Name) values('Mike'); Query OK, 1 row affected ...
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