Execution of complex SQL queries. Operator for data sets INTERSECT Intersect sql examples
- by specifying the tables to join (including subqueries) in the FROM clause of the SELECT statement. First, the tables are joined, and only then the conditions specified by the WHERE clause, aggregation, data ordering, etc., determined by the GROUP BY clause, are applied to the resulting set;
- defining the union of the result sets produced by the processing of the SELECT statement. In this case, the two SELECT statements are joined by the phrase UNION, INTERSECT, EXCEPT or CORRESPONDING .
UNION
Phrase UNION combines the results of two queries according to the following rules:
The standard does not impose any restrictions on the ordering of rows in the result set. So, some DBMS first display the result of the first query, and then the result of the second query. Oracle DBMS automatically sorts records by the first specified column, even if no index has been created for it.
To explicitly specify the required sort order, use the ORDER BY clause. In this case, you can use both the name of the column and its number (Fig. 4.3).
Rice. 4.3.
Phrase UNION ALL performs the union of two subqueries in the same way as the UNION clause, with the following exceptions:
- matching rows are not removed from the generated result set;
- merged queries appear sequentially in the result set without ordering.
When combining more than two queries, parentheses can be used to change the order in which the join operation is performed (Figure 4.4).
Rice. 4.4.
INTERSECT join
Phrase INTERSECT allows you to select only those rows that are present in each result set being merged. On fig. 4.5 shows an example of combining queries as intersecting sets.
Rice. 4.5.
EXCEPT union
Phrase EXCEPT allows you to select only those rows that are present in the first result set to be merged but not present in the second result set.
Phrases INTERSECT and EXCEPT should only be supported at full SQL-92 compliance level. So, some DBMS instead of the phrase
This SQL tutorial explains how to use the SQL INTERSECT operator with syntax and examples.
Description
The SQL INTERSECT operator is used to return the results of 2 or more SELECT statements. However, it only returns the rows selected by all queries or data sets. If a record exists in one query and not in the other, it will be omitted from the INTERSECT results.
Intersect Query
Explanation: The INTERSECT query will return the records in the blue shaded area. These are the records that exist in both Dataset1 and Dataset2.
Each SQL statement within the SQL INTERSECT must have the same number of fields in the result sets with similar data types.
Syntax
The syntax for the INTERSECT operator in SQL is:
SELECT expression1, expression2, ... expression_n FROM tables INTERSECT SELECT expression1, expression2, ... expression_n FROM tables ;
Parameters or Arguments
expression1, expression2, expression_n tables The tables that you wish to retrieve records from. There must be at least one table listed in the FROM clause. WHERE conditions Optional. These are conditions that must be met for the records to be selected.Example - With Single Expression
The following is a SQL INTERSECT operator example that has one field with the same data type:
SELECT supplier_id FROM suppliers INTERSECT SELECT supplier_id FROM orders;
In this SQL INTERSECT example, if a supplier_id appeared in both the suppliers and orders table, it would appear in your result set.
Now, let's compare our example further by adding to the INTERSECT query.
SELECT supplier_id FROM suppliers WHERE supplier_id > 78 INTERSECT SELECT supplier_id FROM orders WHERE quantity<> 0;
In this example, the WHERE clauses have been added to each of the datasets. The first dataset has been filtered so that only records from the suppliers table where the supplier_id is greater than 78 are returned. The second dataset has been filtered so that only records from the orders quantity is not equal to 0.
Example - With Multiple Expressions
Next, let's look at an example of how to use the INTERSECT operator in SQL to return more than one column.
SELECT contact_id, last_name, first_name FROM contacts WHERE last_name<>"Anderson" INTERSECT SELECT customer_id, last_name, first_name FROM customers WHERE customer_id< 50;
In this INTERSECT example, the query will return the records from the contacts table where the contact_id, last_name, and first_name values match the customer_id, last_name, and first_name value from the customers table.
There are WHERE conditions on each data set to further filter the results so that only records from the contacts are returned where the last_name is not Anderson. The records from the customers table are returned where the customer_id is less than 50.
Example - Using ORDER BY
SELECT supplier_id, supplier_name FROM suppliers WHERE supplier_id > 2000 INTERSECT SELECT company_id, company_name FROM companies WHERE company_id > 1000 ORDER BY 2;Since the column names are different between the two SELECT statements, it is more advantageous to reference the columns in the ORDER BY clause by their position in the result set. In this example, we"ve sorted the results by supplier_name / company_name in ascending order, as denoted by the ORDER BY 2 .
The supplier_name / company_name fields are in position #2 in the result set.
When you often come across any technology, programming language, standard, a certain picture of their capabilities is formed, the boundaries in which they are used. This can go on for a long time until examples come across that expand the hardened horizons of knowledge. Today, I would like to talk about such examples and demonstrate them for the SQL language. Interesting and rare designs, forgotten expressions, strange tricks are waiting for you in this article. Who are interested, welcome under cat.Nuances
I am often asked, who is this article for? But, believe me, it is not always easy to give an answer: on the one hand, there are ninja developers who are difficult to surprise with anything, and on the other, young Padawans. But one thing I can say for sure - for a reader who is interested in SQL, who is able to supplement his rich picture with small, but very interesting details. This article will not contain kilometer pages of an sql query, a maximum of 1, 2 lines, and only what is rare in my opinion. But since I want to be completely frank, if you are with sql on you, the article will seem boring. All examples in the article, with the exception of the first and fourth, can be attributed to the SQL-92 standard.Data
In order to make life easier for us, I threw a simple data plate on which certain points will be tested, and for brevity, I will give the result of the experiment on them. I check all requests on PostgreSql.Scripts and data table
CREATE TABLE goods(id bigint NOT NULL, name character varying(127) NOT NULL, description character varying(255) NOT NULL, price numeric(16,2) NOT NULL, articul character varying(20) NOT NULL, act_time timestamp NOT NULL , availability boolean NOT NULL, CONSTRAINT pk_goods PRIMARY KEY (id)); INSERT INTO goods (id, name, description, price, articul, act_time, availability) VALUES (1, "Slippers", "Soft", 100.00, "TR-75", (ts "2017-01-01 01:01: 01.01"), TRUE); INSERT INTO goods (id, name, description, price, articul, act_time, availability) VALUES (2, "Pillow", "White", 200.00, "PR-75", (ts "2017-01-02 02:02: 02.02"), TRUE); INSERT INTO goods (id, name, description, price, articul, act_time, availability) VALUES (3, "Blanket", "Duvet", 300.00, "ZR-75", (ts "2017-01-03 03:03: 03.03"), TRUE); INSERT INTO goods (id, name, description, price, articul, act_time, availability) VALUES (4, "Pillow case", "Grey", 400.00, "AR-75", (ts "2017-01-04 04:04: 04.04"), FALSE); INSERT INTO goods (id, name, description, price, articul, act_time, availability) VALUES (5, "Sheet", "Silk", 500.00, "BR-75", (ts "2017-01-05 05:05: 05.05"), FALSE);
Requests
1. Double quotes
And the first thing I have is a simple question: Could you give an example of a sql query using double quotes? Yes, not with singles, doubles?Example with double quotes
SELECT name "Product name" FROM goods
I was very surprised when I saw it for the first time. If you try to change double quotes to single quotes, the result will be completely different!
It may seem that this is not a very useful example for real development. For me it's not. Now I actively use it in all my sql-blanks. The bottom line is simple, when you return in half a year to a sql-query of 40 columns, oh, how their "our" name saves. Despite the fact that I did not indicate about SQL-92, in the latest edition there is a mention of double quotes.
2. Pseudo table. SQL-92
A little not exactly, in terms of terminology, but the essence is simple - the table resulting from the subquery in the FROM section. Perhaps the most famous fact in this articlePseudo table
SELECT mock.nickname "Nickname", (CASE WHEN mock.huff THEN "Yes" ELSE "No" END) "Huffed?" FROM (SELECT name AS nickname, availability AS huff FROM goods) mock
In our example, the mock is a pseudo table (sometimes called a virtual table). Naturally, they are not intended at all to distort the true meaning. An example is this.
3. Data block constructor. SQL-92
Sounds scary, just because I didn't find a good translation or interpretation. And as always, it's easier to explain with an example:Data block constructor example
SELECT name "Product name", price "Price" FROM (VALUES ("Slippers", 100.00), ("Pillow", 200.00)) AS goods(name, price)
| Product name | Price |
| Slippers | 100.00 |
| Pillow | 200.00 |
In section FROM used keyword VALUES, followed by data in parentheses, line by line. The bottom line is that we do not select data from any table at all, but simply create it on the fly, “name” it a table, name the columns and then use it at our discretion. This thing turned out to be extremely useful when testing different cases of a sql query, when there is no data for some tables (in your local database), and writing insert is too lazy or sometimes very difficult, due to the connection of tables and restrictions.
4. Time, Date and Time-and-Date
Probably everyone has come across in queries, with the need to specify the time, date or date-and-time. Many DBMSs support the literals t, d, and ts, respectively, to work with these types. But it's easier to explain with an example: For the literals d and t, everything is the same.I apologize to the reader for misleading, but everything that is said in paragraph 4 does not apply to the SQL language, but refers to the query preprocessing capabilities in JDBC.
5. Denial. SQL-92
We all know about the operator NOT, but very often forget that it can be applied both to a group of predicates and to a single column:6. Comparison of data blocks. SQL-92
Once again, I apologize for the terminology. This is one of my favorite examples.Data Block Comparison Example
SELECT * FROM goods WHERE (name, price, availability) = ("Pillowcase", 400.00, FALSE) -- or equivalent SELECT * FROM goods WHERE name = "Pillowcase" AND price = 400.00 AND availability = FALSE
As you can see from the example, comparing data blocks is similar to comparing element by element. meaning_ 1 _block_1 = value_ 1 _block_2, value_ 2 _block_1 = value_ 2 _block_2, value_ 3 _block_1 = value_ 3 _block_2 using AND between them.
7. Comparison operators with ANY, SOME or ALL modifiers. SQL-92
This is where an explanation is needed. But as always, first an exampleWhat does it mean ALL in this case? And it means that the selection condition is satisfied only by those rows whose identifiers (in our case, these are 4 and 5) are greater than any from the found values in the subquery (1, 2 and 3). 4 is greater than 1 and than 2 and than 3. 5 is similar. What happens if we replace ALL on the ANY?What does ANY in this case? And it means that the selection condition is satisfied only by those rows whose identifiers (in our case, these are 2, 3, 4 and 5) are greater than at least one from the found values in the subquery (1, 2 and 3). For myself I associated ALL With AND, a ANY With OR. SOME and ANY analogues to each other.
8. Operators for working with requests / under requests. SQL-92
It is enough known that it is possible to combine 2 queries with each other using the operators UNION or UNION ALL. This is often used. But there are 2 more operators EXCEPT and INTERSECT.Example with EXCEPT
Actually, the data of the second set are excluded from the first set of values.
Actually there is an intersection of the first set of values and the second set.
That's all, thank you for your attention.
Editorial
N1. Thanks to streetflush for the constructive criticism. Contributed an article with information about what is a language standard and what is not.N2. Item 4 corrected, with clarification that ts/d/t is not part of the SQL language. Thank you for your attention Melkij.
In that study guide you will learn how to use EXCEPT statement in SQL Server
(Transact-SQL) with syntax and examples.
Description
SQL Server EXCEPT Statement(Transact-SQL) is used to return all rows in the first SELECT statement that are not returned by the second SELECT statement. Each SELECT statement will define a dataset. The EXCEPT statement will extract all records from the first dataset and then remove all records from the second dataset from the results.
Except Request
Explanation: The EXCEPT query will return the entries in the gray shaded area. These are records that exist in SELECT 1 and not in SELECT 2.
Each SELECT statement in an EXCEPT query must have the same number of fields in result sets with similar data types.
Syntax
The syntax for the EXCEPT statement in SQL Server (Transact-SQL) is:
Options or Arguments
expressions are the columns or calculations you want to compare between the two SELECT statements. They do not have to be the same fields in each of the SELECT statements, but the corresponding columns must be of similar data types.
tables - tables from which you want to get records. There must be at least one table listed in the FROM clause.
WHERE conditions - optional. Conditions that must be met for the selected records.
Note
- Both SELECT statements must have the same number of expressions.
- The corresponding columns in each of the SELECT statements must have similar data types.
- The EXCEPT statement returns all records from the first SELECT statement that are not included in the second SELECT statement.
- The EXCEPT statement in SQL Server is equivalent to the MINUS statement in Oracle.
Single expression example
Let's look at an example of an EXCEPT statement in SQL Server (Transact-SQL) that returns a single field with the same data type.
For instance:
Transact SQL
SELECT product_id FROM products EXCEPT SELECT product_id FROM inventory;
SELECT product_id FROM products SELECT product_id FROM inventory ; |
This EXCEPT statement example returns all product_id values that are in the products table and not in the inventory table. This means that if a product_id value exists in the products table and also exists in the inventory table, the product_id value will not appear in the results of an EXCEPT query.
Example with multiple expressions
Next, let's look at an example of an EXCEPT query in SQL Server (Transact-SQL) that returns more than one column.
For instance:
Transact SQL
In this example, the EXCEPT query returns records in the contacts table with the name contact_id , last_name , and first_name , which does not match the employee_id , last_name , and first_name value in the employees table.
