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Update SELECT wiki with set operators.

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go-jet 2019-07-02 10:31:52 +02:00
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wiki/SELECT.md
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@ -2,11 +2,34 @@
SELECT statement is used to retrieve records from one or more tables in PostgreSQL.
More about SELECT statement in postgres can be found at: https://www.postgresql.org/docs/11/sql-select.html
Following clauses are supported:
- SELECT(expressions...) - expressions to form output rows of the SELECT statement.
- DISTINCT() - remove all duplicate rows from result set
- FROM(tableSource...) - specifies one or more source tables for the SELECT.
- WHERE(condition) - only rows for which condition returns true will be selected.
- GROUP BY(groupingElement, ...) - will condense into a single row all selected rows that share the same values for the grouped expressions.
- HAVING(condition) - eliminates group rows that do not satisfy the condition
- ORDER BY(orderBy, ...) - causes the result rows to be sorted according to the specified expression(s)
- LIMIT(count) - specifies the maximum number of rows to return
- OFFSET(start) - specifies the number of rows to skip before starting to return rows
- FOR(lockMode) - how SELECT will lock rows as they are obtained from the table
Lock mode can be:
- jet.UPDATE()
- jet.NO_KEY_UPDATE()
- jet.SHARE()
- jet.KEY_SHARE()
## SELECT statement clauses
Lock mode can be extended with following clauses:
- NOWAIT()
- SKIP_LOCKED()
Following clauses are supported - SELECT, DISTINCT, FROM, WHERE, GROUP BY, HAVING, ORDER BY, LIMIT, OFFSET and FOR.
_This list might be extended with feature Jet releases._
- UNION(select) / UNION_ALL(select) - computes the set union of the rows returned by the involved SELECT statements
- INTERSECT(select) / INTERSECT_ALL(select) - computes the set intersection of the rows returned by the involved SELECT statements
- EXCEPT(select) / EXCEPT_ALL(select) - computes the set of rows that are in the result of the left SELECT statement but not in the result of the right one
_This list might be extended with feature Jet releases._
### Examples per clause
##### 1. SELECT clause
@ -125,16 +148,6 @@ OFFSET 11
##### 9. FOR clause
Lock mode can be:
- jet.UPDATE()
- jet.NO_KEY_UPDATE()
- jet.SHARE()
- jet.KEY_SHARE()
Lock mode has following clauses:
- NOWAIT()
- SKIP_LOCKED()
```
Go:
.FOR(jet.NO_KEY_UPDATE().SKIP_LOCKED())
@ -143,11 +156,31 @@ SQL:
FOR NO KEY UPDATE SKIP LOCKED
```
##### 10. Set clauses (UNION, UNION_ALL, INTERSECT, INTERSECT_ALL, EXCEPT, EXCEPT_ALL)
```
Go:
SELECT(Payment.Amount).FROM(Payment)
UNION_ALL(SELECT(Payment.Amount).FROM(Payment))
Sql:
(
(
SELECT payment.amount AS "payment.amount"
FROM dvds.payment
)
UNION
(
SELECT payment.amount AS "payment.amount"
FROM dvds.payment
)
);
```
### Two forms of select statements in Jet
#### 1. Classical select statement
Columns selected are before tables selected
Columns selected are before table source selected
```
SELECT(
Payment.AllColumns,
@ -160,7 +193,7 @@ LIMIT(30)
```
#### 2. Jet select statement
Joined tables(or just one) are before columns selected. There is no FROM.
Table sources are before columns selected. There is no FROM.
```
Payment.
INNER_JOIN(Customer, Payment.CustomerID.EQ(Customer.CustomerID))