models/bird-sql/knowledge/rules.md

Environment / Tooling

• bash tool executes shell commands mechanically; no auth or gating observed.
• SQLite DB accessed via sqlite3 database.db "<SQL>" in the working directory (also works with ./database.db).
• Schema file ./schema.sql sits alongside database.db and contains only CREATE TABLE statements (no data). May include commented-out columns (e.g. -- PctGE1500 double null) that are NOT in the live table.
• Multiple SQL statements can be issued in one sqlite3 invocation separated by ;; each result set is printed sequentially with no separator (may appear ambiguous, e.g. duplicate - when values overlap between statements).
• Multiple sqlite3 invocations and echo calls can be chained via newline in a single bash command; outputs concatenate in order.
• Default sqlite3 CLI output: pipe-separated columns, newline-separated rows, no header, no row count.
• Backticks embedded in a double-quoted shell argument must be escaped as \``; identifiers can alternatively be quoted with "..."` inside the double-quoted argument.
• SQL errors surface as is_error=True with format Error: in prepare, no such column: <col>\n <query snippet>\n ^--- error here.
• No observed timeouts, rate limits, or output truncation.

Data Integrity

• Foreign-key columns may be NULL (all FK columns declared default NULL).
• Numeric values in the DB can carry floating-point imprecision (e.g. -0.199999999999999 stored as REAL; averages returned to full float precision, e.g. 465.432098765432, 16.7005649717514, 137.888888888889).
• schools.Virtual codes are single letters (e.g. F, P, N) — F observed to mean non-virtual in query contexts (but virtual-named schools like California Virtual Academy also carry Virtual='F', so the code is not a reliable virtual-vs-brick indicator).
• satscores.sname may be NULL or empty string '' (both occur for the same county in results); filter with sname IS NOT NULL AND sname != '' to exclude blanks.
• schools.FundingType may be NULL (blank in output) for schools not in the CS funding model. Distinct non-null values: Directly funded, Locally funded, Not in CS funding model (plus empty).
• schools.AdmEmail1/2/3 may be empty strings for some schools.
• expense.approved observed only as true in the loaded DB (no false rows present).
• atom_id index component is variable width: SUBSTR(atom_id,7,2) returns e.g. 1,2,...,21,22 (trailing chars beyond string end are omitted; no zero-padding). Use range comparisons on the substring as strings only when width is uniform.