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The fourth constraint. `check ( <expr> )` reuses the ADR-0026 WHERE-expression grammar via `Subgrammar`, so a check is written in the same language as a `where` filter. - Grammar: a `CHECK_CONSTRAINT` arm joins the shared constraint-suffix Choice; `consume_check_expr` extracts the parenthesised expression (paren-depth aware) into `ColumnSpec.check` / `Command::AddColumn.check`. - Storage: the parsed `Expr` is compiled once to inline SQL (`compile_check_sql` — `compile_expr` + ADR-0028's param-inliner) and stored in that form everywhere — a new `check_expr` column in `__rdbms_playground_columns`, `project.yaml`'s `ColumnSchema.check`, and the column DDL emitted by `do_create_table` / `schema_to_ddl`. - `add column … check` routes through the rebuild primitive (SQLite's `ALTER … ADD COLUMN` cannot carry it); a CHECK on a serial/shortid column is create-table-only and refused at add-column with a friendly message. - `describe` surfaces the CHECK. ADR-0029 §7/§8 updated to the SQL-form decision — double-quoted identifiers, consistent with ADR-0028's `explain` display SQL. 1201 tests pass (+8); clippy clean.
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2.2 KiB
Simple-mode query limitations
Simple mode's DSL query surface is deliberately a subset of SQL. The DSL is a teaching on-ramp; advanced mode (raw SQL) is the full surface. This document is the running list of what a simple-mode query cannot express that advanced-mode SQL can.
It serves two audiences:
- Students — each entry is the seed of a short explanation of why the boundary exists and what to use instead (often: switch to advanced mode).
- Designers — the consolidated list feeds the future
Q4SQL-subset specification: the inverse view of what the supported subset deliberately leaves out.
The list grows as new simple-mode surface lands; each entry names the ADR that drew the boundary.
WHERE expressions (ADR-0026)
- Comparison operands are a column or a literal, not a
nested expression.
(a > b) = (c > d)— comparing two boolean sub-expressions — cannot be written. Parentheses group boolean sub-expressions, not comparison operands. - A bare column is not a boolean. A predicate always
has an operator: write
Active = true, notActive. - No arithmetic in expressions (
Price * 1.1). - No string concatenation.
- No scalar functions (
upper(Name),length(x), …). - No subqueries, and no
EXISTS.
Query shape (ADR-0026)
- No
ORDER BY.show data … limit <n>orders implicitly by the primary key; explicit ordering is not yet available. - No
LIMIT … OFFSET—limittakes a row count only.
Table creation (ADR-0029)
create tabledeclares only primary-key columns.create table T with pk …makes every listed column part of the primary key; there is no simple-mode syntax for a non-PK column in the same statement. Non-PK columns are added afterward withadd column. Creating a table with a mix of PK and non-PK columns in one statement needs advanced-modeCREATE TABLEsyntax.check (<expr>)constraints reuse the WHERE-expression grammar (ADR-0026), so the same limits apply: no scalar functions (length(x)), no arithmetic. A check is a boolean combination of column-vs-literal comparisons,LIKE,IN,BETWEEN, andIS NULL.