Sql selezione univoca

Esempi di codice

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0

SQL DISTINTO

SELECT DISTINCT column1, column1, ..... FROM TABLE
/*DISTINCT WILL NOT SELECT THE SAME VALUES IN SAME COLUMN*/
1
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sql insert per ogni valore distinto

insert into your_table (col1, col2, col3)
select distinct col1, 'newval', col3
from your_table
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sql insert per ogni valore distinto

insert into your_table (col1, col2, col3)
select distinct col1, 'newval', col3
from your_table
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sql unico

This constraint ensures all values in a column are unique.
Example 1 (MySQL): Adds a unique constraint to the id column when
creating a new users table.
CREATE TABLE IF NOT EXISTS users (
id int NOT NULL,
name varchar(255) NOT NULL,
UNIQUE (id)
);
Example 2 (MySQL): Alters an existing column to add a UNIQUE
constraint.
ALTER TABLE users
ADD UNIQUE (id);
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sql unico

This constraint ensures all values in a column are unique.
Example 1 (MySQL): Adds a unique constraint to the id column when
creating a new users table.
CREATE TABLE IF NOT EXISTS users (
id int NOT NULL,
name varchar(255) NOT NULL,
UNIQUE (id)
);
Example 2 (MySQL): Alters an existing column to add a UNIQUE
constraint.
ALTER TABLE users
ADD UNIQUE (id);
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come selezionare un elemento univoco in sql

DISTINCT
- select distinct * from employees; ==> 
  retrieves any row if it has at
  least a single unique column.

- select distinct first_name from employees; ==> 
      retrieves unique names
     from table. (removes duplicates)
     
- select distinct count(*) from employees;
     retrieve number of unique rows
     if any row has at least a single unique data.
0
0

elemento unico in sql

DISTINCT
- select distinct * from employees; ==> retrieves any row if it has at
least a single unique column.
- select distinct first_name from employees; ==> retrieves unique names
from table. (removes duplicates)
- select distinct count(*) from employees; retrieve number of unique rows
if any row has at least a single unique data.
0
0

sql unica selezionare

SELECT DISTINCT col1, col2, ....
FROM table_name;

SELECT col1, MIN(col2)
FROM table_name
GROUP BY col1;

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