SELECT COUNT (DISTINCT Publication_Date) FROM publication
What is the number of distinct publication dates?
CREATE TABLE "publication" (
"Publication_ID" int,
"Book_ID" int,
"Publisher" text,
"Publication_Date" text,
"Price" real,
PRIMARY KEY ("Publication_ID"),
FOREIGN KEY ("Book_ID") REFERENCES "book"("Book_ID")
);
CREATE TABLE "book" (
"Book_ID" int,
"Title" text,
"Issues" real,
"Writer" text,
PRIMARY KEY ("Book_ID")
);
INSERT INTO  "book" VALUES (1,"The Black Lamb","6","Timothy Truman");
INSERT INTO  "publication" VALUES (1,1,"Pearson","August 2008","15000000");