Answer:
The answer is c. “old-style” join.
Explanation:
SELECT P_CODE, P_DESCRIPT, P_PRICE, V_NAME
FROM PRODUCT, VENDOR
WHERE PRODUCT.V_CODE = VENDOR.V_CODE;
The SELECT clause represents all the columns to be displayed.
The FROM clause represents the tables which are used to extract the columns.
The WHERE clause shows the common column that exists in both the tables. This represents the old-style join when JOIN keyword was not used.
The tables are joined in two ways.
1. Using JOIN keyword
The syntax for this is given as
SELECT column1, column2
FROM table1 JOIN table2
ON table1.column3 = table2.column3;
This returns all rows from two tables having the same value of common column.
Two tables are taken at a time when JOIN keyword is used.
If more tables are to be used, they are mentioned as follows.
SELECT column1, column2
FROM table1 JOIN table2
ON table1.column3 = table2.column3
JOIN table3
ON table3.column4 = table1.column4
( ON table3.column5 = table2.column5 )
The part in italics shows that the third table can either share the same column with table1 or table2.
The given query can be re-written using JOIN as shown.
SELECT P_CODE, P_DESCRIPT, P_PRICE, V_NAME
FROM PRODUCT JOIN VENDOR
ON PRODUCT.V_CODE = VENDOR.V_CODE;
2. Equating common column in WHERE clause
SELECT column1, column2
FROM table1, table2
WHERE table1.column3 = table2.column3;
This returns all rows from two tables having the same value of the common column.
Here, no keyword is used except the general syntax of the query. ON keyword as shown in the above example is replaced with WHERE.
Tables to be used are mentioned in FROM clause separated by commas.
Tables are joined based on the same column having same values.
Multiple tables can be joined using this style as follows.
SELECT column1, column2
FROM table1, table2, table3, table4
WHERE table1.column3 = table2.column3
AND table3.column5=table1.column5
AND table3.column4 = table2.column4;
