Common column data types and table constraints including check, unique, and foreign key, each explained with a short example.
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- What is the CHAR data type used for?
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Fixed-length string storage. Always allocates the specified number of bytes regardless of actual string length.- What is the VARCHAR data type used for?
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Variable-length string storage. Only allocates space for the actual string content, up to a maximum length.- When should you use CHAR instead of VARCHAR?
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When you have fixed-length values, like postal codes (5 digits), state abbreviations (2 letters), or gender codes.- What is the INT data type used for?
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Storing whole numbers. Typically ranges from about -2 billion to +2 billion.- What is the BIGINT data type used for?
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Storing very large whole numbers, ranging from about -9 quintillion to +9 quintillion.- What is the SMALLINT data type used for?
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Storing smaller whole numbers, ranging from about -32,000 to +32,000. Uses less storage than INT.- What is the DECIMAL data type used for?
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Storing exact decimal numbers. Defined with precision (total digits) and scale (digits after decimal point), like DECIMAL(10,2).- What is the FLOAT data type used for?
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Storing approximate decimal numbers using floating-point representation. Takes less storage than DECIMAL but may lose precision.- When should you use DECIMAL instead of FLOAT?
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For financial calculations and any scenario where exact precision is critical. DECIMAL stores values exactly, FLOAT is approximate.- What is the DATE data type used for?
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Storing dates without time information. Format is typically YYYY-MM-DD.- What is the TIME data type used for?
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Storing time without date information. Format is typically HH:MM:SS.- What is the DATETIME data type used for?
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Storing both date and time together. Format is typically YYYY-MM-DD HH:MM:SS.- What is the BOOLEAN data type used for?
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Storing true or false values. Some databases represent this as 1 for true and 0 for false.- What is the TEXT data type used for?
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Storing large amounts of text data. More flexible than VARCHAR and suitable for long documents or descriptions.- What is the BLOB data type used for?
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Storing binary large objects like images, audio, or video files as raw binary data.
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