SQL vs NoSQL

Compare SQL and NoSQL.

NoSQL comparison

NoSQL covers non-relational databases: document, key-value, column-family, graph. SQL demands a strict structure; NoSQL offers a flexible one. The CAP theorem limits you to two of three guarantees.

SELECT data->>'name' FROM documents
WHERE data->>'status' = 'active';

NoSQL offers flexible structure.

data->>'name' is selected from documents. WHERE keeps only the rows where data->>'status' = 'active' holds.

NoSQL comparison — details

CAP: consistency, availability, partition tolerance. During a network partition you pick two. SQL picks consistency + partition tolerance; most NoSQL picks availability + partition tolerance.

Exercise NoSQL comparison

Select data->>'name' from the documents table; return only active documents.

Show example solution

SELECT data->>'name' FROM documents WHERE data->>'status' = 'active';

Test yourself

Document access

SELECT data____'name' FROM documents

Show answer

SELECT data->>'name' FROM documents

SQL vs NoSQL: match the terms

NoSQL

non-relational
document

document
CAP

three guarantees
key-value

key-value
How many guarantees does CAP limit?
- Both of them
- All of them
- Only one of them
- Two of the three
Show answer

Two of the three — CAP limits you to two of three guarantees.

Next lesson: Summary - Distributed and big data

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