Query

Query#

MuduDB supports single-table SELECT queries with a WHERE clause for filtering rows. The query engine evaluates predicates and returns a result set to the caller.

3.1 Overview#

A query in MuduDB is executed in the context of the current transaction. All reads are consistent with the transaction’s isolation level. Results are returned as a row set that the client can iterate over.

The current query capability is intentionally scoped to single-table lookups and scans. Complex analytics, joins, and aggregations are not supported in v0.1.

3.2 Select#

Syntax#

SELECT select_term [, select_term ...]
FROM table_name
[WHERE predicate [AND predicate ...]];

Select Terms#

A select_term is one of:

  • * — select all columns in table order.

  • column_name — select a single column.

  • An arithmetic expression involving columns and literals (e.g., amount * 2, count + 1).

WHERE Predicates#

Each predicate has the form:

expression comparison_operator expression

Comparison operators:

Operator

Meaning

=

Equal

!=

Not equal

<

Less than

<=

Less than or equal

>

Greater than

>=

Greater than or equal

Predicates are combined with the AND logical connective only. OR and NOT are not supported in v0.1.

Expressions#

An expression can be:

  • A column reference

  • A numeric, string, or temporal literal

  • A placeholder (?)

  • An arithmetic expression: +, -, *, / with standard precedence

Examples#

Select all columns:

SELECT * FROM users;

Select specific columns with a filter:

SELECT id, name FROM users WHERE id = 1;

Select with multiple predicates:

SELECT ol_i_id, ol_amount
FROM order_line
WHERE ol_w_id = 1 AND ol_d_id = 2 AND ol_o_id = 100;

Select with placeholders (prepared statement):

SELECT * FROM stock WHERE s_w_id = ? AND s_i_id = ?;

Select with a reversed comparison (parser normalises the shape):

SELECT id FROM users WHERE 7 > id;
-- internally normalised to: id < 7

Select with an arithmetic expression in the term list:

SELECT id, amount * 2 FROM ledger WHERE id = 1;

Unsupported Query Features#

The following are not available in v0.1:

  • JOIN (inner, outer, cross)

  • GROUP BY / HAVING

  • ORDER BY

  • LIMIT / OFFSET

  • DISTINCT

  • Subqueries (SELECT ... FROM (SELECT ...))

  • Window functions

  • Common Table Expressions (WITH)

  • Set operations (UNION, INTERSECT, EXCEPT)