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feat: restructure docs into "chapters" (#12)
* feat(docker, k8s): create containers folder and kubernetes notes
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docs/databases/sql.md
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docs/databases/sql.md
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# SQL
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## DDL
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```sql
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show databases; -- mostra database
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CREATE DATABASE <database>; -- database creation
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use <database_name>; -- usa un database particolare
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exit; -- exit mysql
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show tables; -- mostra tabelle del database
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-- INLINE COMMENT
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/* MULTI-LINE COMMENT */
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```
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### Table Creation
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```sql
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CREATE TABLE <table_name>
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(<field_name> <field_type> <option>,
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...);
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```
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### PRIMARY KEY from multiple fields
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```sql
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CREATE TABLE <table_name>(
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...,
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PRIMARY KEY (<field1>, ...),
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);
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```
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### Table Field Options
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```sql
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PRIMARY KEY -- marks primary key as field option
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NOT NULL -- marks a necessary field
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REFERENCES <table> (<field>) -- adds foreign key reference
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UNIQUE (<field>) -- set field as unique (MySQL)
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<field> UNIQUE -- T-SQL
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```
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### Table Modification
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```sql
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ALTER TABLE <table>
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ADD PRIMARY KEY (<field>, ...), -- definition of PK after table creation
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ADD <field_name> <field_type> <option>; -- addition of a new field, field will have no value in the table
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ALTER TABLE <table>
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CHANGE <field_name> <new_name> <new_type>;
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ALTER COLUMN <field_name> <new_name> <new_type>; -- T-SQL
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ALTER TABLE <table>
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DROP <field>;
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ALTER TABLE <table>
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ADD FOREIGN KEY (<field>) REFERENCES <TABLE> (<FIELD>);
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```
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## DML
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### Data Insertion
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```sql
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INSERT INTO <table> (field_1, ...) VALUES (value_1, ...), (value_1, ...);
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INSERT INTO <table> VALUES (value_1, ...), (value_1, ...); -- field order MUST respect tables's columns order
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```
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### Data Update
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```sql
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UPDATE <table> SET <field> = <value>, <field> = <value>, ... WHERE <condition>;
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```
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### Data Elimination
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```sql
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DELETE FROM <table> WHERE <condition>
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DELETE FROM <table> -- empty the table
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```
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## Data Selection
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`*`: denotes all table fields
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```sql
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SELECT * FROM <table>; -- show table contents
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SHOW columns FROM <table>; -- show table columns
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DESCRIBE <table>; -- shows table
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```
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### Alias
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```sql
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SELECT <field> as <alias>; -- shows <field/funzione> with name <alias>
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```
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### Conditional Selection
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```sql
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SELECT * FROM <table> WHERE <condition>; -- shows elements that satisfy the condition
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AND, OR, NOT -- logic connectors
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SELECT * FROM <table> WHERE <field> Between <value_1> AND <value_2>;
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```
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### Ordering
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```sql
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SELECT * FROM <table> ORDER BY <field>, ...; -- shows the table ordered by <field>
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SELECT * FROM <table> ORDER BY <field>, ... DESC; -- shows the table ordered by <field>, decreasing order
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SELECT * FROM <table> ORDER BY <field>, ... LIMIT n; -- shows the table ordered by <field>, shows n items
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SELECT TOP(n) * FROM <table> ORDER BY <field>, ...; -- T-SQL
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```
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## Grouping
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```sql
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SELECT * FROM <table> GROUP BY <field>;
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SELECT * FROM <table> GROUP BY <field> HAVING <condition>;
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SELECT DISTINCT <field> FROM <table>; -- shows elements without repetitions
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```
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### Ricerca caratteri in valori
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`%`: any number of characters
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```sql
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SELECT * FROM <table> WHERE <field> LIKE '<char>%'; -- selects items in <field> that start with <char>
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SELECT * FROM <table> WHERE <field> LIKE '%<char>'; -- selects items in <field> that end with <char>
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SELECT * FROM <table> WHERE <field> LIKE '%<char>%'; -- selects items in <field> that contain <char>
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SELECT * FROM <table> WHERE <field> NOT LIKE '%<char>%'; -- selects items in <field> that do not contain <char>
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```
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### Selection from multiple tables
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```sql
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SELECT a.<field>, b.<field> FROM <table> AS a, <table> AS b
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WHERE a.<field> ...;
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```
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## Functions
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```sql
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SELECT COUNT(*) FROM <field>; -- count of items in <field>
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SELECT MIN(*) FROM <table>; -- min value
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SELECT MAX(*) FROM <table>; -- max value
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SELECT AVG(*) FROM <table>; -- mean of values
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ALL (SELECT ...)
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ANY (SELECT ...)
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```
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## Nested Queries
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```sql
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SELECT * FROM <table> WHERE EXISTS (SELECT * FROM <table>) -- selected field existing in subquery
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SELECT * FROM <table> WHERE NOT EXISTS (SELECT * FROM <table>) -- selected field not existing in subquery
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```
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## New table from data
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Create new table with necessary fields:
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```sql
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CREATE TABLE <table> (
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(<field_name> <field_type> <option>,
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...);
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)
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```
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Fill fields with data from table:
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```sql
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INSERT INTO <table>
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SELECT <fields> FROM <TABLE> WHERE <condition>;
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```
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## Join
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```sql
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SELECT * FROM <table1> JOIN <table2> ON <table1>.<field> = <table2>.<field>;
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SELECT * FROM <table1> LEFT JOIN <table2> ON <condition>;
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SELECT * FROM <table1> RIGHT JOIN <table2> ON <condition>
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```
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[Inner Join, Left Join, Right Join, Full Outer Join](https://www.diffen.com/difference/Inner_Join_vs_Outer_Join)
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## Multiple Join
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```sql
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SELECT * FROM <table1>
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JOIN <table2> ON <table1>.<field> = <table2>.<field>
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JOIN <table3> ON <table2>.<field> = <table3>.<field>;
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```
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[char, nchar, varchar, nvarchar](https://stackoverflow.com/questions/176514/what-is-the-difference-between-char-nchar-varchar-and-nvarchar-in-sql-server)
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---
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## T-SQL (MSSQL Server)
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### T-SQL Insert From table
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```sql
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USE [<db_name>]
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SET IDENTITY_INSERT [<destination_table>] ON
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INSERT INTO <table> (field_1, ...)
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SELECT (field_1, ...) FROM <source_table>
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SET IDENTITY_INSERT [<destination_table>] OFF
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```
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### T-SQL Parametric Query
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```sql
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-- variable declaration
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DECLARE @var_name <type>
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-- init variable (input parameter)
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SET @var_name = <value>
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-- use in query (memorize data)
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SELECT @var_name = COUNT(*) -- query won't show results in the "table view" since param is used in SELECT
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FROM <table> ...
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-- display message (query won't show results in the "table view")
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PRINT 'Text: ' + @var_name
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PRINT 'Text: ' + CONVERT(type, @var_name) -- convert data before printing
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GO
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```
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### T-SQL View
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A view represents a virtual table. Join multiple tables in a view and use the view to present the data as if the data were coming from a single table.
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```sql
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CREATE VIEW <name> AS
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SELECT * FROM <table> ...
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```
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### T-SQL Stored Procedure
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[Stored Procedure How-To](https://docs.microsoft.com/en-us/sql/relational-databases/stored-procedures/create-a-stored-procedure "Create a Stored Procedure - Microsoft Docs")
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[T-SQL Stored Procedure](https://docs.microsoft.com/en-us/sql/t-sql/statements/create-procedure-transact-sql)
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Stored Procedure Definition:
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```sql
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CREATE PROCEDURE <Procedure_Name>
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-- Add the parameters for the stored procedure here
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<@Param1> <Datatype_For_Param1> = <Default_Value_For_Param1>,
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<@Param2> <Datatype_For_Param2>
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AS
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BEGIN
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-- SET NOCOUNT ON added to prevent extra result sets from interfering with SELECT statements.
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SET NOCOUNT ON; -- don't return number of selected rows
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-- Insert statements for procedure here
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SELECT ...
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END
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GO
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```
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Stored Procedure call in query:
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```sql
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USE <database>
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GO
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-- Stored Procedure call
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EXECUTE <Procedure_Name>
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-- or
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EXEC <Procedure_Name>
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```
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