背景-
一般来说，我对postgres和sql非常陌生。我正在完成一项家庭作业，在将erd导出为sql并在postgres中运行之前，我们必须将包含数据和概念的6x.csv文件以erd的形式作为表。
我的sql脚本-
--员工职称表

CREATE TABLE "titles" (
    "title_id" VARCHAR   NOT NULL,
    "title" VARCHAR   NOT NULL
);

-- Employees Table
CREATE TABLE "employees" (
    "emp_no" INT   NOT NULL,
    "emp_title_id" INT   NOT NULL,
    "birth_date" DATE   NOT NULL,
    "first_name" VARCHAR   NOT NULL,
    "last_name" VARCHAR   NOT NULL,
    "sex" INT   NOT NULL,
    "hire_date" DATE   NOT NULL,
    CONSTRAINT "pk_employees" PRIMARY KEY (
        "emp_no"
     )
);

-- Salaries Table
CREATE TABLE "salaries" (
    "emp_no" INT   NOT NULL,
    "salary" INT   NOT NULL
);

-- Department Manager
CREATE TABLE "dept_manager" (
    "dept_no" VARCHAR   NOT NULL,
    "emp_no" INT   NOT NULL
);

-- Department Numbers
CREATE TABLE "departments" (
    "dept_no" VARCHAR   NOT NULL,
    "dept_name" VARCHAR   NOT NULL,
    CONSTRAINT "pk_departments" PRIMARY KEY (
        "dept_no"
     )
);

-- Employee vs. Department
CREATE TABLE "dept_emp" (
    "emp_no" INT   NOT NULL,
    "dept_no" VARCHAR   NOT NULL
);

ALTER TABLE "employees" ADD CONSTRAINT "fk_employees_emp_title_id" FOREIGN KEY("emp_title_id")
REFERENCES "titles" ("title_id");

ALTER TABLE "salaries" ADD CONSTRAINT "fk_salaries_emp_no" FOREIGN KEY("emp_no")
REFERENCES "employees" ("emp_no");

ALTER TABLE "dept_manager" ADD CONSTRAINT "fk_dept_manager_dept_no" FOREIGN KEY("dept_no")
REFERENCES "departments" ("dept_no");

ALTER TABLE "dept_manager" ADD CONSTRAINT "fk_dept_manager_emp_no" FOREIGN KEY("emp_no")
REFERENCES "employees" ("emp_no");

ALTER TABLE "dept_emp" ADD CONSTRAINT "fk_dept_emp_emp_no" FOREIGN KEY("emp_no")
REFERENCES "employees" ("emp_no");

ALTER TABLE "dept_emp" ADD CONSTRAINT "fk_dept_emp_dept_no" FOREIGN KEY("dept_no")
REFERENCES "departments" ("dept_no");

问题
我可以很好地导出sql脚本，但是当我运行

ALTER TABLE "employees" ADD CONSTRAINT "fk_employees_emp_title_id" FOREIGN KEY("emp_title_id")
REFERENCES "titles" ("title_id");

“我收到错误信息error:there is 对于引用的表“titles”sql state:42830，没有与给定键匹配的唯一约束
我的想法-
…这可能是titles表中外键之间的名称不匹配吗( title_id )它是employees表中的主键( emp_title_id )导致了这个问题。两者 title_id 以及 emp_title_id 包含相同的值（即雇员id，例如s0002）。