Difference between INSERT INTO and INSERT ALL INTO - sql

Question

While I was inserting some records in table i found that..
INSERT INTO T_CANDYBAR_DATA
SELECT CONSUMER_ID,CANDYBAR_NAME,SURVEY_YEAR,GENDER,1 AS STAT_TYPE,OVERALL_RATING
FROM CANDYBAR_CONSUMPTION_DATA
UNION
SELECT CONSUMER_ID,CANDYBAR_NAME,SURVEY_YEAR,GENDER,2 AS STAT_TYPE,NUMBER_BARS_CONSUMED
FROM CANDYBAR_CONSUMPTION_DATA;
79 rows inserted.
INSERT ALL
INTO t_candybar_data VALUES (consumer_id,candybar_name,survey_year,gender,1,overall_rating)
INTO t_candybar_data VALUES (consumer_id,candybar_name,survey_year,gender,2,number_bars_consumed)
SELECT * FROM candybar_consumption_data
86 rows inserted.
I have read somewhere that INSERT ALL INTO automatically unions then why those difference is showing.

Answer 1

The problem is your queries are different—your first is with UNION and your second is without—so they are naturally inserting different numbers of values. As far as what INSERT ALL is versus a straight INSERT:
INSERT can be used for inserting new records to a single table.
INSERT ALL can be used for inserting new records to multiple tables based on the query condition.
So your assumption as stated here:
I have read somewhere that INSERT ALL INTO automatically unions then
why those difference is showing.
Is incorrect. INSERT ALL doesn’t have anything to do with UNION in any way. But that said, you might be mixing up UNION ALL as explained here.
The SQL UNION ALL operator is used to combine the result sets of 2 or
more SELECT statements. It returns all rows from the query (even if
the row exists in more than one of the SELECT statements).
Each SELECT statement within the UNION ALL must have the same number
of fields in the result sets with similar data types.