Add SQL Explore docs (#29)

docs/guides/web_ui/04_explore.md

@@ -1,2 +1,140 @@
-!!! warning "🚧 Work in Progress 🚧"
-    This page is yet to be written, [contact us](../../help.md) if you have any questions.
+With **Logfire**, you can use the Explore page to run arbitrary SQL queries against your trace and metric data to
+analyze and investigate your system.
+
+![Logfire explore screen](../../images/guide/browser-explore-full.png)
+
+## Querying Traces
+
+The primary table you will query is the `records` table, which contains all the spans/logs from your traced requests.
+
+To query the records, simply start your query with `SELECT ... FROM records` and add a `WHERE` clause to filter the
+spans you want.
+
+For example, here is a query that returns the message, start_timestamp, duration, and attributes for all spans that
+have exceptions:
+
+```sql
+SELECT
+  message,
+  start_timestamp,
+  EXTRACT(EPOCH FROM (end_timestamp - start_timestamp)) * 1000 AS duration_ms,
+  attributes
+FROM records
+WHERE is_exception
+```
+
+You can run more complex queries as well, using subqueries, CTEs, joins, aggregations, custom expressions,
+and any other standard SQL.
+
+## Records Schema
+
+The schema of the `records` table is:
+
+```sql
+CREATE TABLE records AS (
+    start_timestamp timestamp with time zone,
+    created_at timestamp with time zone,
+    trace_id text,
+    span_id text,
+    parent_span_id text,
+    kind span_kind,
+    end_timestamp timestamp with time zone,
+    level smallint,
+    span_name text,
+    message text,
+    attributes_json_schema text,
+    attributes jsonb,
+    tags text[],
+    otel_links jsonb,
+    otel_events jsonb,
+    is_exception boolean,
+    otel_status_code status_code,
+    otel_status_message text,
+    otel_scope_name text,
+    otel_scope_version text,
+    otel_scope_attributes jsonb,
+    service_namespace text,
+    service_name text,
+    service_version text,
+    service_instance_id text,
+    process_pid integer
+)
+```
+
+## Cross-linking with Live View
+
+After running a query, you can take any `trace_id` and/or `span_id` and use it to look up data shown as traces
+in the Live View.
+
+Simply go to the Live View and enter a query like:
+
+```
+trace_id = '7bda3ddf6e6d4a0c8386093209eb0bfc' -- replace with a real trace_id of your own
+```
+
+This will show all the spans with that specific trace ID.
+
+## Metrics Schema
+
+In addition to traces, you can also query your metrics data using the `metrics` table.
+
+The schema of the `metrics` table is:
+
+```sql
+CREATE TABLE metrics AS (
+    recorded_timestamp timestamp with time zone,
+    metric_name text,
+    metric_type text,
+    unit text,
+    start_timestamp timestamp with time zone,
+    aggregation_temporality public.aggregation_temporality,
+    is_monotonic boolean,
+    metric_description text,
+    scalar_value double precision,
+    histogram_min double precision,
+    histogram_max double precision,
+    histogram_count integer,
+    histogram_sum double precision,
+    exp_histogram_scale integer,
+    exp_histogram_zero_count integer,
+    exp_histogram_zero_threshold double precision,
+    exp_histogram_positive_bucket_counts integer[],
+    exp_histogram_positive_bucket_counts_offset integer,
+    exp_histogram_negative_bucket_counts integer[],
+    exp_histogram_negative_bucket_counts_offset integer,
+    histogram_bucket_counts integer[],
+    histogram_explicit_bounds double precision[],
+    attributes jsonb,
+    tags text[],
+    otel_scope_name text,
+    otel_scope_version text,
+    otel_scope_attributes jsonb,
+    service_namespace text,
+    service_name text,
+    service_version text,
+    service_instance_id text,
+    process_pid integer
+)
+```
+
+You can query metrics using standard SQL, just like traces. For example:
+
+```sql
+SELECT *
+FROM metrics
+WHERE metric_name = 'system.cpu.time'
+  AND recorded_timestamp > now() - interval '1 hour'
+```
+
+## Executing Queries
+
+To execute a query, type or paste it into the query editor and click the "Run Query" button.
+
+![Logfire explore screen](../../images/guide/browser-explore-run-query.png)
+
+You can modify the time range of the query using the dropdown next to the button. There is also a "Limit" dropdown that
+controls the maximum number of result rows returned.
+
+The Explore page provides a flexible interface to query your traces and metrics using standard SQL.
+
+Happy querying! :rocket: