Add examples

20230204224830_examples.down.sql

@@ -0,0 +1,4 @@
+BEGIN;
+DROP TABLE example_texts;
+DROP TABLE examples;
+COMMIT;

20230204224830_examples.up.sql

@@ -0,0 +1,20 @@
+BEGIN;
+
+CREATE TABLE examples (
+    id BIGSERIAL PRIMARY KEY
+);
+
+CREATE TABLE example_texts (
+    id BIGSERIAL PRIMARY KEY,
+    example_id BIGINT NOT NULL REFERENCES examples (id),
+    language_id BIGINT NOT NULL REFERENCES languages (id),
+    index BIGINT NOT NULL,
+    value TEXT NOT NULL,
+    CONSTRAINT index_is_not_negative CHECK(index >= 0),
+    CONSTRAINT value_is_sane_text CHECK (is_sane_text(value))
+);
+
+CREATE UNIQUE INDEX example_texts_example_language_index
+    ON example_texts (example_id, language_id, index);
+
+COMMIT;