doc: add query to get skill condition types

doc/README.md

@@ -228,6 +228,63 @@ tag_id is a slash-separated list of numeric IDs that roughly describe all effect
 - 614 base stat threshold passive
 - 615 mood passive
 
+unrelated, query to get all condition types:
+```sql
+WITH RECURSIVE condition AS (
+    SELECT DISTINCT precondition_1 AS c FROM skill_data
+    UNION
+    SELECT DISTINCT condition_1 AS c FROM skill_data
+    UNION
+    SELECT DISTINCT precondition_2 AS c FROM skill_data
+    UNION
+    SELECT DISTINCT condition_2 AS c FROM skill_data
+), disj AS (
+    SELECT
+        IIF(INSTR(c, '@') != 0, SUBSTR(c, 1, INSTR(c, '@')-1), c) AS c,
+        IIF(INSTR(c, '@') != 0, SUBSTR(c, 1 + INSTR(c, '@')), '') AS rest
+    FROM condition
+    UNION
+    SELECT
+        IIF(INSTR(rest, '@') != 0, SUBSTR(rest, 1, INSTR(rest, '@')-1), rest) AS c,
+        IIF(INSTR(rest, '@') != 0, SUBSTR(rest, 1 + INSTR(rest, '@')), '') AS rest
+    FROM disj
+    WHERE rest != ''
+), term AS (
+    SELECT
+        IIF(INSTR(c, '&') != 0, SUBSTR(c, 1, INSTR(c, '&')-1), c) AS term,
+        IIF(INSTR(c, '&') != 0, SUBSTR(c, 1 + INSTR(c, '&')), '') AS rest
+    FROM disj
+    UNION
+    SELECT
+        IIF(INSTR(rest, '&') != 0, SUBSTR(rest, 1, INSTR(rest, '&')-1), rest) AS term,
+        IIF(INSTR(rest, '&') != 0, SUBSTR(rest, 1 + INSTR(rest, '&')), '') AS rest
+    FROM term
+    WHERE rest != ''
+), op AS (
+    SELECT
+        term,
+        CASE
+            WHEN INSTR(term, '==') != 0 THEN '=='
+            WHEN INSTR(term, '!=') != 0 THEN '!='
+            WHEN INSTR(term, '<=') != 0 THEN '<='
+            WHEN INSTR(term, '>=') != 0 THEN '>='
+            WHEN INSTR(term, '<') != 0 THEN '<'
+            WHEN INSTR(term, '>') != 0 THEN '>'
+        END AS op
+    FROM term WHERE term != ''
+), type_op_arg AS (
+    SELECT DISTINCT
+        term,
+        SUBSTR(term, 1, INSTR(term, op) - 1) AS "type",
+        op,
+        CAST(SUBSTR(term, INSTR(term, op) + LENGTH(op)) AS INTEGER) AS arg
+    FROM op
+)
+SELECT DISTINCT CONCAT(type, op), arg FROM type_op_arg
+```
+
+final select can be adjusted to get different info, but type+op together seems most useful
+
 # races
 
 - group 1, grade: g1 100, g2 200, g3 300, op 400, pre-op 700