#POSTGRESQL WHERE UPDATE#

The reason being as previously mentioned GROUP BY also works as the distinct condition.

The thing to note here there is only a single entry for India though there are two records in the original data set. Internally, to begin with two groups are created one each for Cricket and Football and then based on these groups the next set of groups with respect to the column 'winner' are created. In order to achieve this we add a GROUP BY clause with respect to the column 'sports_name' and winner. select sports_name,winner from worldcuphistory When we use GROUP BY Col1, Col2, the query basically puts all those rows with the same values for both Col1 and Col2 in one group. In this example, our idea is to accumulate all the winners of cricket world cup in one group and all the winners of football world cup in another group. To illustrate the next couple of scenarios, we will use the following table:Įxample 2: GROUP BY clause on multiple columns We have removed the other columns, as any column not included in the GROUP BY needs to be included in an aggregate function. The remaining rows fall into these two groups. If we add the GROUP BY, notice that only two rows are displayed. This statement basically works as a distinct condition, which removes duplicate date from the result set. We can see all the data here. The basic syntax is as shown here: SELECT col1,lNĮxample 1: GROUP BY clause without aggregate function The GROUP BY clause works with aggregates functions, like SUM(), COUNT() and also without aggregate functions. The GROUP BY clause comes after the WHERE clause and before the ORDER BY clause. This is used to reduce the redundancy in the result. The PostgreSQL GROUP BY clause is used with SELECT statements to accumulate identical data into groups. select * from employees order by age asc, employee_id desc The ASC keyword is optional, and is used here to maintain clarity. The ordering for each column can be set individually by using the ASC or DESC keyword with respect to each column after the ORDER BY statement. This example it is possible to sort the result set by multiple columns. select * from employees order by employee_id desc In this example the Order By clause sorts the result set based on the column employee id in descending order because of the explicit mention of the keyword, DESC, after the ORDER BY clause. In this query, we see that the results will be sorted on the column age and in ascending order. Note, each column listed should have the ASC or DESC keyword after it to explicitly set the ordering. The basic syntax for the ORDER BY clause is: SELECT col1,lN We shall next see some examples to better understand the functionality. To sort the result set in descending order, the keyword, DESC, needs to be explicitly mentioned after the column used in the ORDER BY clause. The ORDER BY clause by default sorts the result set in ascending order, and the ASC keyword need not be explicitly mentioned.

#POSTGRESQL WHERE UPDATE#

The ORDER BY clause cannot be directly used in an UPDATE or DELETE statement, however, they can part of the sub-select that are in an UPDATE or DELETE statement. By default the select statement fetches the rows in an undetermined order therefore the ORDER BY clause is used for enforce some ordering of the rows in the result set. The ORDER BY clause is used for sorting the rows returned by the SELECT statement in either ascending or descending order. DELETE FROM employees WHERE employee_id=2 This removes the row(s) where the employee id is 2. UPDATE employees SET age=35,gender='M' where employee_id=3 In this example we update the age and gender of the employee whose employee id is 3, setting them to 35 and M, respectively. Similarly other filter criteria can also be used after the Where clause to filter the data. In this example we retrieve the details of the employee whose employee id is 1. In the Select command the Where condition is used to filter rows returned by the Select statement. Use any of these to select the appropriate criteria data to work with in your query. The WHERE clause can be used with logical and comparison operators like AND, OR, =,, or !=, >=, <=, IN, LIKE, BETWEEN, NOT, IS NULL. UPDATE table_name SET column1 = value1, column2 = value2. The WHERE clause is used to filter the output when used in collaboration with Select, Update or Delete Statement. The basic syntax is: SELECT col1, col2. In this first chapter of the tutorial we will cover Where, Order By, Group By clauses with suitable example. There are various database clauses available in PostgreSQL, like Where, Order By, Group By, Having, Distinct, Limit, Fetch. A database clause is a conditional statement used to filter data from the database.

Postgresql where