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Once there's data in the table, we might find that there is a need to modify the data. To do so, we can use the UPDATE command. The syntax for this is
SET "column_1" = [new value]
For example, say we have a table as below:
and we notice that the sales for Los Angeles on Jan-08-1999 is actually $500 instead of $300, and that particular entry needs to be updated. To do so, we use the following SQL query:
SET Sales = 500
WHERE Store_Name = 'Los Angeles'
AND Txn_Date = 'Jan-08-1999';
The resulting table would look like
In this case, there is only one row that satisfies the condition in the WHERE clause. If there are multiple rows that satisfy the condition, all of them will be modified. If no WHERE clause is specified, all rows will be modified.
Update Multiple Columns
It is also possible to UPDATE multiple columns at the same time. The syntax in this case would look like the following:
SET column_1 = [value1], column_2 = [value2]
For example, let's say we notice that the 'San Diego' entry has the wrong Sales and TXN_Date information. To fix it, we run the following SQL statement:
SET Sales = 600, Txn_Date = 'Jan-15-1999'
WHERE Store_Name = 'San Diego';
The table now becomes,
IMPORTANT: When using the UPDATE statement, pay special attention to make sure that condition is specified. Otherwise, the value of all rows can be changed.
1. Using the same Store_Information table right above, what data is in the table after the following SQL statement is executed?
2. Continuing to use the same table. What is the content of the table after the following SQL statement is executed?
3. Again using the same table. What is the content of the table after the following SQL statement is executed?