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1. Top results related to what do you mean by constraint in sql

   • What do we mean by SQL NOW() and created_at in SQL

     Top Answer

     Answered Jul 18, 2018 · 1 votes

     This is a bit long for a comment.

     This is a strange way to write the condition. I think it is easier to follow as:

     select *from otp_logwhere verified_at is NULL and created_at > now() - ? and email_otp = ? and mobile_otp = ?

     I don't know what 300,4906,20102 is supposed to be. If it is present in the query, then it would cause a syntax error. Otherwise, the "No rows found" means just what it says: no rows match the where conditions.

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     1/5

   • what do you mean by select 1 from sysobjects..?

     Top Answer

     Answered Mar 26, 2018 · 1 votes

     The intent of given snippet is to ensure database tabel does not exist after it's ran. It achieves this by checking if table exists from system metainfo and dropping the table if it was found.

     sysobjects is a the system table which according to documentation:

     Contains one row for each object that is created within a database, such as a constraint, default, log, rule, and stored procedure.

     According the doc linked above table named "test" is represented in that table by type = 'U' AND name = 'test'. Since we only care about the existence of a row and no actual value is needed then we are selecting any small contant value, hence select 1. It could also have been select 'yabadabadoo'if you liked it more.

     Also, note documentation emphasizes that given table sysobjects is deprecated and should not be used anymore and hints that you should use view sys.objects instead.

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     2/5

   • What do you do in SQL Server to CREATE OR ALTER?

     Top Answer

     Answered Aug 13, 2019 · 113 votes

     This article makes a good point about losing permissions when dropping an object in SQL server.

     • Tips ‘N’ Tricks – T-SQL – An Elegant way to CREATE or ALTER Stored Procedures in One-Go for Easy Maintenance

     So here is the approach which retains permissions:

     IF OBJECT_ID('spCallSomething') IS NULL EXEC('CREATE PROCEDURE spCallSomething AS SET NOCOUNT ON;')GOALTER PROCEDURE spCallSomething ... --instead of DROP/CREATE

     Also works for functions, just replace PROCEDURE with FUNCTION in the above code.

     Another reason to consider doing it this way is tolerance to failure. Suppose your DROP succeeds, but your CREATE fails - you end with a broken DB. Using ALTER approach, you will end up with an older version of the object.

     Other Answers

     Answered Jun 20, 2020 · 69 votes

     The year is 2009 and SQL Server does not have CREATE OR ALTER/REPLACE.

     The year is 2016 and it does now have DIE (Drop If Exists) in SQL Server 2016 RTM and CREATE OR ALTER (introduced in 2016 SP1).

     Taking Drop If Exists first the caveats around needing to re-apply permissions with this approach still apply. Example syntax is

     DROP PROCEDURE IF EXISTS dbo.SynchronizeRemoteCatalogGOCREATE PROCEDURE dbo.SynchronizeRemoteCatalogAS BEGIN BODY: END GO/*TODO: Reapply permissions*/

     CREATE OR ALTER retains the permissions. Example syntax is

     CREATE OR ALTER PROCEDURE dbo.SynchronizeRemoteCatalog AS BEGIN BODY: END

     The corresponding MSSQL Tiger Team blog post explains

     CREATE OR ALTER can be used in programmability objects such as:

     • STORED PROCEDURES (including natively compiled)
     • FUNCTIONS (Transact-SQL, including natively compiled)
     • TRIGGERS
     • VIEWS

     But cannot be used in:

     • Objects that require storage (tables, indexes and indexed views)
     • CLR user-defined functions
     • Deprecated programmability objects (RULE and DEFAULT)
     • ["Non-programmability objects (such as CREATE ASSEMBLY, CREATE TABLE or CREATE - SCHEMA). On these objects, the syntax for CREATE and","ALTER is very different from a syntax and usability perspective."]

     Other Answers

     Answered Jul 15, 2016 · 6 votes

     We encountered a situation where we needed to update a remote site, but we didn’t have DROP permissions. Until now, we have been using the ‘DROP and CREATE’ script built into SSMS 2008 R2, but now we needed to change. We created three templates, which we drop above the appropriate ALTER scripts when we need to update a stored procedure or function:

     —- Stored ProcedureIF OBJECT_ID('[dbo].[<Name_Of_Routine, , >]') IS NULLEXEC('CREATE PROCEDURE [dbo].[<Name_Of_Routine, , >] AS SET NOCOUNT ON;')EXEC('GRANT EXECUTE ON [<Name_Of_Routine, , >] TO Public AS dbo;')GO—- Scalar FunctionIF OBJECT_ID('[dbo].[<Name_Of_Routine, , >]') IS NULLEXEC('CREATE FUNCTION [dbo].[<Name_Of_Routine, , >] (@i INT) RETURNS INT AS BEGIN RETURN 0 END;')EXEC('GRANT EXECUTE ON [<Name_Of_Routine, , >] TO Public AS dbo;')GO—- Table-based FunctionIF OBJECT_ID('[dbo].[<Name_Of_Routine, , >]') IS NULLEXEC('CREATE FUNCTION [dbo].[<Name_Of_Routine, , >] (@i INT) RETURNS @O TABLE(i INT) AS BEGIN INSERT INTO @O SELECT 0 RETURN END;')GO

     Any special permissions get scripted after each CREATE (Table functions cannot be assigned permissions). After that, the ALTER doesn’t change it, and if they add or modify the permissions, they remain. Doing it this way, it’s an easy task to copy the name of the function or stored procedure, and use the Template Parameter replacement to automating the completion of these scriptlets.

     Now, I’m hoping that the good folks at Microsoft will either add this to their “Script ___ as” lists, or give us the ability to create our own such that this scripting comes ‘baked-in’

     You may want to throw some weight behind the SQL Server feedback entry at: https://connect.microsoft.com/SQLServer/feedback/details/344991/create-or-alter-statement. It seems to be one of the few that are still accessible publicly, and they state that they "have started a feasibility review for this to decide if we can ship this in the near future." The more voices, the more likely this will happen!

     (Update: now also using the following code for Triggers and Views)

     -- TriggersIF OBJECT_ID('[dbo].[<Name_Of_Trigger, , >]') IS NULL -- Check if Trigger Exists EXEC('CREATE TRIGGER [dbo].[<Name_Of_Trigger, , >] ON [<Name_Of_Table, , >] AFTER UPDATE AS SET NOCOUNT ON;') -- Create dummy/empty SPGO-- ViewsIF OBJECT_ID('[dbo].[<Name_Of_View, , >]') IS NULL -- Check if View Exists EXEC('CREATE VIEW [dbo].[<Name_Of_View, , >] AS SELECT 1;') -- Create dummy/empty ViewGO

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     3/5

   • What do you call the . syntax in SQL?

     Top Answer

     Answered Jul 19, 2022 · 1 votes

     These are typically called "qualified" and names, and they can be used when an "unqualified" name is ambiguous, for example when a select query pulls data from multiple tables that share column names.

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     4/5

   • What do brackets mean around column names in SQL Server?

     Top Answer

     Answered Aug 23, 2010 · 28 votes

     Columns enclosed in square brackets are usually keywords or contain special characters or spaces.

     What specific column name do you have enclosed in brackets?

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     5/5

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2. www.w3schools.com › sql › sql_constraintsSQL Constraints - W3Schools

   www.w3schools.com › sql › sql_constraints

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   SQL constraints are used to specify rules for the data in a table. Constraints are used to limit the type of data that can go into a table. This ensures the accuracy and reliability of the data in the table. If there is any violation between the constraint and the data action, the action is aborted. Constraints can be column level or table level.

   • SQL Not Null

     SQL NOT NULL Constraint. By default, a column can hold NULL...

   • SQL Check

     SQL CHECK Constraint. The CHECK constraint is used to limit...

3. learnsql.com › blog › what-is-sql-constraintWhat Is a SQL Constraint? | LearnSQL.com

   learnsql.com › blog › what-is-sql-constraint

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   • Understanding SQL Constraints
   • Examples of SQL Constraints
   • Using SQL Constraints
   • SQL Constraints Are A Powerful Tool

   A SQL constraint is a rule for ensuring the correctness of data in a table. Frequently used SQL constraints include: 1. NOT NULL– The column value cannot be empty (i.e. cannot contain a null value). 2. UNIQUE– The column cannot contain duplicate values (i.e. all values in the column must be different). 3. PRIMARY KEY– Each column value must uniquel...

   See full list on learnsql.com

   Let’s go through all the most common SQL constraints one by one. Each of them is explained with an example.

   See full list on learnsql.com

   When to Use SQL Constraints

   There are a number of situations when we should use SQL constraints to ensure data correctness. In this section, I’ll summarize all the SQL constraints that we’ve learned and implement our first real-world example. Let’s imagine that we have a table called Clients: When this table was created, we set up rules that must be followed by any application trying to manipulate this table’s data. These rules are: 1. The Id column is the PRIMARY KEY. It uniquely identifies each client record and canno...

   Why Use SQL Constraints?

   The usage of SQL constraints ensures that: 1. Data is correct (appropriate to the column). 2. Data is of good quality (no information is missing or of the wrong data type). 3. The applications that input the data must conform to the rules/constraints we set. By using SQL constraints, we save time spent checking that the data has the required correctness. Constraints ensure that if future INSERTs or UPDATEs do not conform to the rules, they will not be added to our database.

   Adding Constraints: Modifying Table Definitions with DDL

   We can modify a table’s SQL constraints using the ALTER statement with the ADD CONSTRAINT clause. The ALTER statement must consider the current data in the table. It can’t contradict existing data, e.g. if column X contains duplicate values, we cannot set a UNIQUEconstraint on this column unless the duplicates are removed. Let’s see an example of altering constraints. First, we’ll make a table without any kind of constraint: The above table does not implement any of the SQL constraints. Howev...

   See full list on learnsql.com

   SQL constraints allow you to impose certain conditions and rules on your data, helping you to ensure its accuracy and completeness. Let’s quickly summarize what the different constraints do: 1. UNIQUEmakes sure all column values are different. 2. NOT NULLforces each field to have a value. 3. CHECKallows you to set customized constraints. 4. DEFAULT...

   See full list on learnsql.com

4. People also ask

   What are SQL constraints?

   • Frequently used SQL constraints include: NOT NULL – The column value cannot be empty (i.e. cannot contain a null value). UNIQUE – The column cannot contain duplicate values (i.e. all values in the column must be different). PRIMARY KEY – Each column value must uniquely identify that row in the table.

   What Is a SQL Constraint? | LearnSQL.com

   learnsql.com/blog/what-is-sql-constraint/

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   What is a constraint in a relational database?

   • A constraint is a rule in a relational database that you create to make sure that data stored in a table adheres to specific standards that you set, such as always making sure there is a value in a particular column, or that the data in a column has to be unique from all other values that are stored.

   What is a SQL Constraint - Null, Check, Default, Unique, Primary Key

   www.mssqltips.com/sqlservertip/7547/what-is-a-sql-constraint/

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   What is a key constraint in SQL Server?

   • They are: Primary Key Constraint: this ensures all rows have a unique value and cannot be NULL, often used as an identifier of a table’s row. Foreign Key Constraint: this ensures that values in a column (or several columns) match values in another table’s column/s. Unique Constraint: this ensures all rows have a unique value.

   SQL Constraints: The Complete Guide - Database Star

   www.databasestar.com/sql-constraints/

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   What is a unique constraint in SQL?

   • What is it? A unique constraint is a type of constraint in SQL databases. It defines a field or set of fields where the combination must be unique in a table. So, if you create a unique constraint on one column, all of the values in that column must be unique.

   SQL Constraints: The Complete Guide - Database Star

   www.databasestar.com/sql-constraints/

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5. www.geeksforgeeks.org › sql-constraintsSQL | Constraints - GeeksforGeeks

   www.geeksforgeeks.org › sql-constraints

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   • Video Duration: 17 min

   • NOT NULL. If we specify a field in a table to be NOT NULL. Then the field will never accept null value. That is, you will be not allowed to insert a new row in the table without specifying any value to this field.
   • UNIQUE. This constraint helps to uniquely identify each row in the table. i.e. for a particular column, all the rows should have unique values. We can have more than one UNIQUE columns in a table.
   • PRIMARY KEY. Primary Key is a field which uniquely identifies each row in the table. If a field in a table as primary key, then the field will not be able to contain NULL values as well as all the rows should have unique values for this field.
   • FOREIGN KEY. Foreign Key is a field in a table which uniquely identifies each row of a another table. That is, this field points to primary key of another table.

6. www.mssqltips.com › 7547 › what-is-a-sql-constraintWhat is a SQL Constraint - Null, Check, Default, Unique ...

   www.mssqltips.com › 7547 › what-is-a-sql-constraint

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   • Author: Joe Gavin

   • Not Null Constraint. A Not Null Constraint ensures that a column cannot have a null value, which is generally considered a column level constraint. T-SQL syntax to create a database table called Employees with three fields that all allow nulls.
   • Check Constraint. A Check Constraint limits the values that can be stored in a column. We'll create a new table called Employees_3. It's safe to assume that anyone we hire would be less than 100 years old at the time of hire.
   • Default Constraint. A Default Constraint will put a default value in a column if it is not specified, unlike a Not Null Constraint which will not allow the operation.
   • Unique Constraint. A Unique Constraint will not allow a duplicate value in a column. We will an additional field called EmpNum, which is used as a unique identifier.

7. www.sqltutorial.net › constraintsSQL constraints – SQL Tutorial

   www.sqltutorial.net › constraints

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   SQL constraints are rules enforced on data columns in SQL Server databases. They ensure the accuracy and reliability of the data in the database. By restricting the type of data that can be stored in a particular column, constraints prevent invalid data entry, which is crucial for maintaining the overall quality of the database.

8. www.databasestar.com › sql-constraintsSQL Constraints: The Complete Guide - Database Star

   www.databasestar.com › sql-constraints

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   Oct 11, 2022 · A constraint is a rule that you define on a table that restricts the values in that table. They can be added to a table or a view when you create it, or after it’s created. You do this by specifying a few keywords and some information about the columns and rules you want to set.

9. www.programiz.com › sql › constraintsSQL Constraints (With Examples) - Programiz

   www.programiz.com › sql › constraints

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   For example, if a column has NOT NULL constraint, it means the column cannot store NULL values. The constraints used in SQL are: Constraint. Description. NOT NULL. values cannot be null. UNIQUE. values cannot match any older value. PRIMARY KEY.