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SQL Tutorial

SQL HOMESQL IntroSQL SyntaxSQL SelectSQL Select DistinctSQL WhereSQL Order BySQL AndSQL OrSQL NotSQL Insert IntoSQL Null ValuesSQL UpdateSQL DeleteSQL Select TopSQL Aggregate FunctionsSQL Min and MaxSQL CountSQL SumSQL AvgSQL LikeSQL WildcardsSQL InSQL BetweenSQL AliasesSQL JoinsSQL Inner JoinSQL Left JoinSQL Right JoinSQL Full JoinSQL Self JoinSQL UnionSQL Union AllSQL Group BySQL HavingSQL ExistsSQL Any, AllSQL Select IntoSQL Insert Into SelectSQL CaseSQL Null FunctionsSQL Stored ProceduresSQL CommentsSQL Operators

SQL Database

SQL Create DBSQL Drop DBSQL Backup DBSQL Create TableSQL Drop TableSQL Alter TableSQL ConstraintsSQL Not NullSQL UniqueSQL Primary KeySQL Foreign KeySQL CheckSQL DefaultSQL IndexSQL Auto IncrementSQL DatesSQL ViewsSQL InjectionSQL HostingSQL Data Types

SQL References

SQL KeywordsMySQL Functions
String Functions:ASCIICHAR_LENGTHCHARACTER_LENGTHCONCATCONCAT_WSFIELDFIND_IN_SETFORMATINSERTINSTRLCASELEFTLENGTHLOCATELOWERLPADLTRIMMIDPOSITIONREPEATREPLACEREVERSERIGHTRPADRTRIMSPACESTRCMPSUBSTRSUBSTRINGSUBSTRING_INDEXTRIMUCASEUPPERNumeric Functions:ABSACOSASINATANATAN2AVGCEILCEILINGCOSCOTCOUNTDEGREESDIVEXPFLOORGREATESTLEASTLNLOGLOG10LOG2MAXMINMODPIPOWPOWERRADIANSRANDROUNDSIGNSINSQRTSUMTANTRUNCATEDate Functions:ADDDATEADDTIMECURDATECURRENT_DATECURRENT_TIMECURRENT_TIMESTAMPCURTIMEDATEDATEDIFFDATE_ADDDATE_FORMATDATE_SUBDAYDAYNAMEDAYOFMONTHDAYOFWEEKDAYOFYEAREXTRACTFROM_DAYSHOURLAST_DAYLOCALTIMELOCALTIMESTAMPMAKEDATEMAKETIMEMICROSECONDMINUTEMONTHMONTHNAMENOWPERIOD_ADDPERIOD_DIFFQUARTERSECONDSEC_TO_TIMESTR_TO_DATESUBDATESUBTIMESYSDATETIMETIME_FORMATTIME_TO_SECTIMEDIFFTIMESTAMPTO_DAYSWEEKWEEKDAYWEEKOFYEARYEARYEARWEEKAdvanced Functions:BINBINARYCASECASTCOALESCECONNECTION_IDCONVCONVERTCURRENT_USERDATABASEIFIFNULLISNULLLAST_INSERT_IDNULLIFSESSION_USERSYSTEM_USERUSERVERSION
SQL Server FunctionsMS Access FunctionsSQL Quick Ref

SQL Examples

SQL ExamplesSQL EditorSQL QuizSQL ExercisesSQL ServerSQL SyllabusSQL Study PlanSQL BootcampSQL CertificateSQL Training

SQLALTER Keyword

ALTER TABLE

TheALTER TABLE command adds, deletes, or modifies columns in a table.

TheALTER TABLE command also adds and deletes various constraints in a table.

The following SQL adds an "Email" column to the "Customers" table:

Example

ALTER TABLE Customers
ADD Email varchar(255);

The following SQL deletes the "Email" column from the "Customers" table:

Example

ALTER TABLE Customers
DROP COLUMN Email;

ALTER COLUMN

TheALTER COLUMN command is used to change the data type of a column in a table.

The following SQL changes the data type of the column named "BirthDate" in the "Employees" table to type year:

Example

ALTER TABLE Employees
ALTER COLUMN BirthDate year;

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