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Database Articles
Page 467 of 547
Perform search/replace for only the first occurrence of a character with session variable in MySQL
To perform search/ replace for only the first occurrence, use the CONCAT and REPLACE() function.The query is as follows to set user defined session variable −mysql> set @Sentence='Thks ks is a my string'; Query OK, 0 rows affected (0.00 sec)In this k will be replaced with i only once. The query is as follows. We have used INSTR() also −mysql> select @Sentence as NewString ,CONCAT(REPLACE(LEFT(@Sentence, INSTR(@Sentence, 'k')), 'k', 'i'), -> SUBSTRING(@Sentence, INSTR(@Sentence, 'k') + 1)) as ChangeOnlyOneTime;The following is the output displaying only the first occurrence of a character is replaced −+------------------------+------------------------+ | NewString ...
Read MoreHow to select part of a Timestamp in a MySQL Query?
To select part of a timestamp in a query, you need to use YEAR() function. The syntax is as follows in MySQL.select YEAR(yourTimestampColumnName) as anyAliasName from yourTableName;To understand the above syntax, let us create a table. The query to create a table is as follows −mysql> create table SelectPartOfTimestampDemo -> ( -> Id int NOT NULL AUTO_INCREMENT PRIMARY KEY, -> ShippingTime TIMESTAMP -> ); Query OK, 0 rows affected (1.11 sec)Now you can insert some records in the table using insert command. The query is as follows −mysql> ...
Read MoreHow to select all rows from a table except the last one in MySQL?
You need to use != operator along with subquery. The syntax is as follows −select *from yourTableName where yourIdColumnName != (select max(yourIdColumnName) from yourTableName );To understand the above syntax, let us create a table. The query to create a table is as follows −mysql> create table AllRecordsExceptLastOne -> ( -> Id int NOT NULL AUTO_INCREMENT, -> UserName varchar(10), -> UserAge int -> , -> PRIMARY KEY(Id) -> ); Query OK, 0 rows affected (0.65 sec)Now you can insert some records in the table using insert command. The query is as follows −mysql> ...
Read MoreResolve ERROR 1111 (HY000): Invalid use of group function in MySQL? How to correctly use aggregate function with where clause?
To correctly use aggregate function with where clause in MySQL, the following is the syntax −select *from yourTableName where yourColumnName > (select AVG(yourColumnName) from yourTableName);To understand the above concept, let us create a table. The query to create a table is as follows −mysql> create table EmployeeInformation -> ( -> EmployeeId int, -> EmployeeName varchar(20), -> EmployeeSalary int, -> EmployeeDateOfBirth datetime -> ); Query OK, 0 rows affected (1.08 sec)Now you can insert some records in the table using insert command. The query is as follows −mysql> insert into EmployeeInformation values(101, 'John', 5510, '1995-01-21'); ...
Read MoreSearching BETWEEN dates stored as varchar in MySQL?
You can search between dates stored as varchar using STR_TO_DATE(). The syntax is as follows −select *from yourTableName where STR_TO_DATE(LEFT(yourColumnName, LOCATE('', yourColumnName)), '%m/%d/%Y') BETWEEN 'yourDateValue1' AND 'yourDateValue2’;To understand the above syntax, let us create a table. The query to create a table is as follows −mysql> create table SearchDateAsVarchar -> ( -> Id int NOT NULL AUTO_INCREMENT, -> ShippingDate varchar(100), -> PRIMARY KEY(Id) -> ); Query OK, 0 rows affected (0.99 sec)Insert some records in the table using INSERT command. The query is as follows −mysql> insert into SearchDateAsVarchar(ShippingDate) values('6/28/2011 9:58 AM'); Query OK, 1 ...
Read MoreSet the MySQL primary keys auto increment to be unlimited (or incredibly huge)?
You can use BIGINT but this is not unlimited but you can use large number of primary keys auto increment using it. The syntax is as follows −yourColumnName BIGINT NOT NULL AUTO_INCREMENT;To understand the above syntax, let us create a table. The query to create a table is as follows −mysql> create table LargeAutoIncrement -> ( -> Id BIGINT NOT NULL AUTO_INCREMENT PRIMARY KEY -> ); Query OK, 0 rows affected (0.78 sec)Now in this table you can store large number like 9223372036854775807 i.e. for primary key auto increment.Let us insert ...
Read MoreCreate a column on my table that allows null but is set by default to empty (not null)?
You need to use default keyword for this. The syntax is as follows −alter table yourTableName add yourColumnName yourDataType NULL Default '';To understand the above syntax, let us create a table. The query to create a table is as follows −mysql> create table AllowNullDefaulNotNullDemo -> ( -> Id int NOT NULL AUTO_INCREMENT, -> UserName varchar(20), -> PRIMARY KEY(Id) -> ); Query OK, 0 rows affected (0.65 sec)Let us add a new column that allow NULL value but default value set to NOT NULL. The query is as follows −mysql> alter table AllowNullDefaulNotNullDemo add UserAddress varchar(20) ...
Read MoreFind document with array that contains a specific value in MongoDB
You can use find() method to find document with array that contains a specific value. The syntax is as follows:db.yourCollectionName.find({"yourArrayFieldName":"yourValue"}, .......N).pretty();To understand the above syntax, let us create a collection with documents. The query to create a collection with documents is as follows:>db.findSpecificValue.insertOne({"StudentId":1, "StudentName":"Larry", "FavouriteSubject":["C", "C++", "Java"]}); { "acknowledged" : true, "insertedId" : ObjectId("5c6e8996140577d89182b8d0") } >db.findSpecificValue.insertOne({"StudentId":2, "StudentName":"Larry", "FavouriteSubject":["MongoDB", "MySQL", "SQL Server"]}); { "acknowledged" : true, "insertedId" : ObjectId("5c6e89b1140577d89182b8d1") }Display all documents from a collection with the help of find() method. The query is as follows:> db.findSpecificValue.find().pretty();The following is the output:{ "_id" : ObjectId("5c6e8996140577d89182b8d0"), "StudentId" ...
Read MoreGet the strings in the table records that ends with numbers?
You need to use REGEXP for this. The syntax is as follows −select *from yourTableName where yourColumnName REGEXP '[[:digit:]]$';To understand the above syntax, let us create a table. The query to create a table is as follows −mysql> create table StringEndsWithNumber -> ( -> Id int NOT NULL AUTO_INCREMENT PRIMARY KEY, -> UserId varchar(20), -> UserName varchar(20) -> ); Query OK, 0 rows affected (0.62 sec)Insert some records in the table using insert command. The query is as follows −mysql> insert into StringEndsWithNumber(UserId, UserName) values('123User', 'John'); Query OK, 1 row affected (0.18 sec) mysql> insert ...
Read MoreGet the date/time of the last change to a MySQL database?
You can get the date/time of the last change to a MySQL database with the help of INFORMATION_SCHEMA.TABLES. The syntax is as follows −SELECT update_time FROM information_schema.tables WHERE table_schema = 'yourDatabaseName’' AND table_name = 'yourTableName’;To understand the above syntax, let us create a table. The query to create a table is as follows −mysql> create table TblUpdate -> ( -> Id int not null auto_increment primary key, -> Name varchar(20) -> ); Query OK, 0 rows affected (0.49 sec)Insert some records in the table using insert command. The query is as follows −mysql> insert into TblUpdate(Name) ...
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