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I read some articles but really didn't understand what does select 1 from do? Someone says "you should use select 1 instead of select *". Here is an example table:
cust_id cust_name cust_address 1000000001 Village Toys Mapl 1000000002 Kids Place South 1000000003 Fun4All Sunny 1000000004 Fun4All Riverside 1000000005 The Toy Store 53rd What will the result be when I write select 1 from customer_table what does this statement do?
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In your case, SELECT 1 FROM DUAL; will simply returns 1 . You need it because the INSERT ALL syntax demands a SELECT clause but you are not querying the input values from a table.
An asterisk (" * ") can be used to specify that the query should return all columns of the queried tables. SELECT is the most complex statement in SQL, with optional keywords and clauses that include: The FROM clause, which indicates the table(s) to retrieve data from.
Hi, Select * from any table will fetch and display all the column in that table, while Select 1 from any table will display one row with 1 without any column name.
WHERE 1 is a synonym for "true" or "everything." It's a shortcut so they don't have to remove the where clause from the generated SQL.
select 1 from table will return a column of 1's for every row in the table. You could use it with a where statement to check whether you have an entry for a given key, as in:
if exists(select 1 from table where some_column = 'some_value') What your friend was probably saying is instead of making bulk selects with select * from table, you should specify the columns that you need precisely, for two reasons:
1) performance & you might retrieve more data than you actually need.
2) the query's user may rely on the order of columns. If your table gets updated, the client will receive columns in a different order than expected.
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