Add translations

20230218130437_translations.down.sql

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+BEGIN;
+DROP TABLE translation_texts;
+DROP TABLE translations;
+COMMIT;

20230218130437_translations.up.sql

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+BEGIN;
+
+CREATE TABLE translations (
+--  name    type      constraints
+    id      BIGSERIAL PRIMARY KEY,
+    word_id BIGINT    NOT NULL REFERENCES words (id),
+    index   BIGINT    NOT NULL,
+
+--  CONSTRAINT name                  CHECK (condition)
+    CONSTRAINT index_is_not_negative CHECK (index >= 0)
+);
+
+CREATE TABLE translation_texts (
+--  name           type      constraints
+    id             BIGSERIAL PRIMARY KEY,
+    translation_id BIGINT    NOT NULL REFERENCES translations (id),
+    lang_id        BIGINT    NOT NULL REFERENCES languages (id),
+    value          TEXT      NOT NULL,
+
+--  CONSTRAINT name               CHECK (condition)
+    CONSTRAINT value_is_sane_text CHECK (is_sane_text(value))
+);
+
+CREATE UNIQUE INDEX translations_word_index ON translations (word_id, index);
+CREATE UNIQUE INDEX translation_texts_translation_lang
+    ON translation_texts (translation_id, lang_id);
+
+COMMIT;