Database Redesign
What SQL command can be used to add columns to a table?

MODIFY TABLE TableName ADD COLUMN ColumnName
MODIFY TABLE TableName ADD ColumnName
ALTER TABLE TableName ADD COLUMN ColumnName
ALTER TABLE TableName ADD ColumnName

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Database Redesign
The EXISTS keyword will be true if:

any row in the subquery meets the condition only.
neither of these two conditions is met.
all rows in the subquery fail the condition only.
both of these two conditions are met.

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