# Query Guide
A practical guide to querying Markdown with mq-db.
## SQL Queries
mq-db supports a subset of SQL executed by a custom evaluator — no SQLite required.
### Basic SELECT
```sql
SELECT id, block_type, content FROM blocks LIMIT 10;
```
### Filtering by Type
```sql
SELECT content, depth FROM blocks
WHERE block_type = 'heading'
ORDER BY pre;
```
### Aggregation
```sql
SELECT block_type, count(*) AS total
FROM blocks
GROUP BY block_type
ORDER BY total DESC;
```
### Joining Documents
```sql
SELECT d.path, b.content
FROM blocks b
JOIN documents d ON d.id = b.document_id
WHERE b.block_type = 'heading' AND b.depth = 1;
```
### Hierarchy with under()
The `under()` function performs an O(1) ancestor check using the interval index.
```sql
SELECT b.block_type, b.content
FROM blocks b
WHERE under(
b.pre, b.post,
(SELECT pre FROM blocks WHERE block_type = 'heading' AND content = 'Architecture'),
(SELECT post FROM blocks WHERE block_type = 'heading' AND content = 'Architecture')
)
ORDER BY b.pre;
```
### Inline mq with mq()
Run an mq program against Markdown content directly inside SQL.
```sql
WHERE block_type = 'code' AND lang = 'markdown';
```
## mq Queries
mq-lang is a jq-inspired query language for Markdown blocks.
### Select Headings
```mq
.h1
.h2
.h
```
### Filter by Property
```mq
select(.code_lang == "rust")
select(.depth == 2)
### Combine Filters
```mq
## DDL — Custom Tables
### Create from Query
```sql
CREATE TABLE headings AS
SELECT content, depth FROM blocks WHERE block_type = 'heading';
```
### Explicit Schema
```sql
CREATE TABLE notes (id TEXT, body TEXT);
INSERT INTO notes VALUES ('1', 'First note');
INSERT INTO notes VALUES ('2', 'Second note');
```
### Inspect and Drop
```sql
SHOW TABLES;
DESC notes;
DROP TABLE notes;
```
## Output Formats
Every query command supports `--format`:
| Table (default) | `--format table` |
| JSON | `--format json` |
| CSV | `--format csv` |
| TSV | `--format tsv` |
| Markdown | `--format markdown` |
| HTML | `--format html` |
```bash
mq-db sql "SELECT * FROM blocks LIMIT 5" --db store.mq-db --format json
mq-db mq ".h1" --db store.mq-db --format markdown
```
